**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.**

Testing Rails Applications
==========================

This guide explores how to write tests in Rails.

After reading this guide, you will know:

* Rails testing terminology.
* How to write unit, functional, integration, and system tests for your
  application.
* Other popular testing approaches and plugins.

--------------------------------------------------------------------------------

Why Write Tests?
----------------

Writing automated tests can be a faster way of ensuring your code continues to
work as expected than manual testing through the browser or the console. Failing
tests can quickly reveal issues, allowing you to identify and fix bugs early in
the development process. This practice not only improves the reliability of your
code but also improves confidence in your changes.

Rails makes it easy to write tests. You can read more about Rails' built in
support for testing in the next section.

Introduction to Testing
-----------------------

With Rails, testing is central to the development process right from the
creation of a new application.

### Test Setup

Rails creates a `test` directory for you as soon as you create a Rails project
using `bin/rails new` _application_name_. If you list the contents of this directory
then you will see:

```bash
$ ls -F test
application_system_test_case.rb  controllers/                     helpers/                         mailers/                         system/                          fixtures/                        integration/                     models/                          test_helper.rb
```

### Test Directories

The `helpers`, `mailers`, and `models` directories store tests for [view
helpers](#testing-view-helpers), [mailers](#testing-mailers), and
[models](#testing-models), respectively.

The `controllers` directory is used for
[tests related to controllers](#functional-testing-for-controllers), routes, and
views, where HTTP requests will be simulated and assertions made on the
outcomes.

The `integration` directory is reserved for [tests that cover
interactions between controllers](#integration-testing).

The `system` test directory holds [system tests](#system-testing), which are
used for full browser testing of your application. System tests allow you to
test your application the way your users experience it and help you test your
JavaScript as well. System tests inherit from
[Capybara](https://github.com/teamcapybara/capybara) and perform in-browser
tests for your application.

[Fixtures](https://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html)
are a way of mocking up data to use in your tests, so that you don't have to use
'real' data. They are stored in the `fixtures` directory, and you can read more
about them in the [Fixtures](#fixtures) section below.

A `jobs` directory will also be created for your job tests when you first
[generate a job](active_job_basics.html#create-the-job).

The `test_helper.rb` file holds the default configuration for your tests.

The `application_system_test_case.rb` holds the default configuration for your
system tests.

### The Test Environment

By default, every Rails application has three environments: development, test,
and production.

Each environment's configuration can be modified similarly. In this case, we can
modify our test environment by changing the options found in
`config/environments/test.rb`.

NOTE: Your tests are run under `RAILS_ENV=test`. This is set by Rails automatically.

### Writing Your First Test

We introduced the `bin/rails generate model` command in the [Getting Started
with Rails](getting_started.html#creating-a-database-model) guide.
Alongside creating a model, this command also creates a test stub in the `test`
directory:

```bash
$ bin/rails generate model article title:string body:text
...
create  app/models/article.rb
create  test/models/article_test.rb
...
```

The default test stub in `test/models/article_test.rb` looks like this:

```ruby
require "test_helper"

class ArticleTest < ActiveSupport::TestCase
  # test "the truth" do
  #   assert true
  # end
end
```

A line by line examination of this file will help get you oriented to Rails
testing code and terminology.

```ruby
require "test_helper"
```

Requiring the file, `test_helper.rb`, loads the default configuration to run
tests. All methods added to this file are also available in tests when this file
is included.

```ruby
class ArticleTest < ActiveSupport::TestCase
  # ...
end
```

This is called a test case, because the `ArticleTest` class inherits from
`ActiveSupport::TestCase`. It therefore also has all the methods from
`ActiveSupport::TestCase` available to it. [Later in this
guide](#assertions-in-test-cases), we'll see some of the methods this gives us.

Any method defined within a class inherited from `Minitest::Test` (which is the
superclass of `ActiveSupport::TestCase`) that begins with `test_` is simply
called a test. So, methods defined as `test_password` and `test_valid_password`
are test names and are run automatically when the test case is run.

Rails also adds a `test` method that takes a test name and a block. It generates
a standard `Minitest::Unit` test with method names prefixed with `test_`,
allowing you to focus on writing the test logic without having to think about
naming the methods. For example, you can write:

```ruby
test "the truth" do
  assert true
end
```

Which is approximately the same as writing this:

```ruby
def test_the_truth
  assert true
end
```

Although you can still use regular method definitions, using the `test` macro
allows for a more readable test name.

NOTE: The method name is generated by replacing spaces with underscores. The
result does not need to be a valid Ruby identifier, as Ruby allows any string to
serve as a method name, including those containing punctuation characters. While
this may require using `define_method` and `send` to define and invoke such
methods, there are few formal restrictions on the names themselves.

This part of a test is called an 'assertion':

```ruby
assert true
```

An assertion is a line of code that evaluates an object (or expression) for
expected results. For example, an assertion can check:

* does this value equal that value?
* is this object nil?
* does this line of code throw an exception?
* is the user's password greater than 5 characters?

Every test may contain one or more assertions, with no restriction as to how
many assertions are allowed. Only when all the assertions are successful will
the test pass.

#### Your First Failing Test

To see how a test failure is reported, you can add a failing test to the
`article_test.rb` test case. In this example, it is asserted that the article
will not save without meeting certain criteria; hence, if the article saves
successfully, the test will fail, demonstrating a test failure.

```ruby#4-7
require "test_helper"

class ArticleTest < ActiveSupport::TestCase
  test "should not save article without title" do
    article = Article.new
    assert_not article.save
  end
end
```

Here is the output if this newly added test is run:

```bash
$ bin/rails test test/models/article_test.rb
Running 1 tests in a single process (parallelization threshold is 50)
Run options: --seed 44656

# Running:

F

Failure:
ArticleTest#test_should_not_save_article_without_title [/path/to/blog/test/models/article_test.rb:4]:
Expected true to be nil or false


bin/rails test test/models/article_test.rb:4



Finished in 0.023918s, 41.8090 runs/s, 41.8090 assertions/s.

1 runs, 1 assertions, 1 failures, 0 errors, 0 skips
```

In the output, `F` indicates a test failure. The section under `Failure`
includes the name of the failing test, followed by a stack trace and a message
showing the actual value and the expected value from the assertion. The default
assertion messages offer just enough information to help identify the error. For
improved readability, every assertion allows an optional message parameter to
customize the failure message, as shown below:

```ruby
test "should not save article without title" do
  article = Article.new
  assert_not article.save, "Saved the article without a title"
end
```

Running this test shows the friendlier assertion message:

```
Failure:
ArticleTest#test_should_not_save_article_without_title [/path/to/blog/test/models/article_test.rb:6]:
Saved the article without a title
```

To get this test to pass a model-level validation can be added for the `title`
field.

```ruby
class Article < ApplicationRecord
  validates :title, presence: true
end
```

Now the test should pass, as the article in our test has not been initialized
with a `title`, so the model validation will prevent the save. This can be
verified by running the test again:

```bash
$ bin/rails test test/models/article_test.rb:6
Running 1 tests in a single process (parallelization threshold is 50)
Run options: --seed 31252

# Running:

.

Finished in 0.027476s, 36.3952 runs/s, 36.3952 assertions/s.

1 runs, 1 assertions, 0 failures, 0 errors, 0 skips
```

The small green dot displayed means that the test has passed successfully.

TIP: In the process above, a test was written first which fails for a desired
functionality, then after, some code was written which adds the functionality.
Finally, the test was run again to ensure it passes. This approach to software
development is referred to as _Test-Driven Development_ (TDD).

#### Reporting Errors

To see how an error gets reported, here's a test containing an error:

```ruby
test "should report error" do
  # some_undefined_variable is not defined elsewhere in the test case
  some_undefined_variable
  assert true
end
```

Now you can see even more output in the console from running the tests:

```bash
$ bin/rails test test/models/article_test.rb
Running 2 tests in a single process (parallelization threshold is 50)
Run options: --seed 1808

# Running:

E

Error:
ArticleTest#test_should_report_error:
NameError: undefined local variable or method 'some_undefined_variable' for #<ArticleTest:0x007fee3aa71798>
    test/models/article_test.rb:11:in 'block in <class:ArticleTest>'


bin/rails test test/models/article_test.rb:9

.

Finished in 0.040609s, 49.2500 runs/s, 24.6250 assertions/s.

2 runs, 1 assertions, 0 failures, 1 errors, 0 skips
```

Notice the 'E' in the output. It denotes a test with an error. The green dot
above the 'Finished' line denotes the one passing test.

NOTE: The execution of each test method stops as soon as any error or an
assertion failure is encountered, and the test suite continues with the next
method. All test methods are executed in random order. The
[`config.active_support.test_order`][] option can be used to configure test
order.

When a test fails you are presented with the corresponding backtrace. By
default, Rails filters the backtrace and will only print lines relevant to your
application. This eliminates noise and helps you to focus on your code. However,
in situations when you want to see the full backtrace, set the `-b` (or
`--backtrace`) argument to enable this behavior:

```bash
$ bin/rails test -b test/models/article_test.rb
```

If you want this test to pass you can modify it to use `assert_raises` (so you
are now checking for the presence of the error) like so:

```ruby
test "should report error" do
  # some_undefined_variable is not defined elsewhere in the test case
  assert_raises(NameError) do
    some_undefined_variable
  end
end
```

This test should now pass.

[`config.active_support.test_order`]:
    configuring.html#config-active-support-test-order

### Minitest Assertions

By now you've caught a glimpse of some of the assertions that are available.
Assertions are the foundation blocks of testing. They are the ones that actually
perform the checks to ensure that things are going as planned.

Here's an extract of the assertions you can use with
[`minitest`](https://github.com/minitest/minitest), the default testing library
used by Rails. The `[msg]` parameter is an optional string message you can
specify to make your test failure messages clearer.

| Assertion                                                      | Purpose |
| -------------------------------------------------------------- | ------- |
| `assert(test, [msg])`                                          | Ensures that `test` is true.|
| `assert_not(test, [msg])`                                      | Ensures that `test` is false.|
| `assert_equal(expected, actual, [msg])`                        | Ensures that `expected == actual` is true.|
| `assert_not_equal(expected, actual, [msg])`                    | Ensures that `expected != actual` is true.|
| `assert_same(expected, actual, [msg])`                         | Ensures that `expected.equal?(actual)` is true.|
| `assert_not_same(expected, actual, [msg])`                     | Ensures that `expected.equal?(actual)` is false.|
| `assert_nil(obj, [msg])`                                       | Ensures that `obj.nil?` is true.|
| `assert_not_nil(obj, [msg])`                                   | Ensures that `obj.nil?` is false.|
| `assert_empty(obj, [msg])`                                     | Ensures that `obj` is `empty?`.|
| `assert_not_empty(obj, [msg])`                                 | Ensures that `obj` is not `empty?`.|
| `assert_match(regexp, string, [msg])`                          | Ensures that a string matches the regular expression.|
| `assert_no_match(regexp, string, [msg])`                       | Ensures that a string doesn't match the regular expression.|
| `assert_includes(collection, obj, [msg])`                      | Ensures that `obj` is in `collection`.|
| `assert_not_includes(collection, obj, [msg])`                  | Ensures that `obj` is not in `collection`.|
| `assert_in_delta(expected, actual, [delta], [msg])`            | Ensures that the numbers `expected` and `actual` are within `delta` of each other.|
| `assert_not_in_delta(expected, actual, [delta], [msg])`        | Ensures that the numbers `expected` and `actual` are not within `delta` of each other.|
| `assert_in_epsilon(expected, actual, [epsilon], [msg])`        | Ensures that the numbers `expected` and `actual` have a relative error less than `epsilon`.|
| `assert_not_in_epsilon(expected, actual, [epsilon], [msg])`    | Ensures that the numbers `expected` and `actual` have a relative error not less than `epsilon`.|
| `assert_throws(symbol, [msg]) { block }`                       | Ensures that the given block throws the symbol.|
| `assert_raises(exception1, exception2, ...) { block }`         | Ensures that the given block raises one of the given exceptions.|
| `assert_instance_of(class, obj, [msg])`                        | Ensures that `obj` is an instance of `class`.|
| `assert_not_instance_of(class, obj, [msg])`                    | Ensures that `obj` is not an instance of `class`.|
| `assert_kind_of(class, obj, [msg])`                            | Ensures that `obj` is an instance of `class` or is descending from it.|
| `assert_not_kind_of(class, obj, [msg])`                        | Ensures that `obj` is not an instance of `class` and is not descending from it.|
| `assert_respond_to(obj, symbol, [msg])`                        | Ensures that `obj` responds to `symbol`.|
| `assert_not_respond_to(obj, symbol, [msg])`                    | Ensures that `obj` does not respond to `symbol`.|
| `assert_operator(obj1, operator, [obj2], [msg])`               | Ensures that `obj1.operator(obj2)` is true.|
| `assert_not_operator(obj1, operator, [obj2], [msg])`           | Ensures that `obj1.operator(obj2)` is false.|
| `assert_predicate(obj, predicate, [msg])`                      | Ensures that `obj.predicate` is true, e.g. `assert_predicate str, :empty?`|
| `assert_not_predicate(obj, predicate, [msg])`                  | Ensures that `obj.predicate` is false, e.g. `assert_not_predicate str, :empty?`|
| `assert_error_reported(class) { block }`                       | Ensures that the error class has been reported, e.g. `assert_error_reported IOError { Rails.error.report(IOError.new("Oops")) }`|
| `assert_no_error_reported { block }`                           | Ensures that no errors have been reported, e.g. `assert_no_error_reported { perform_service }`|
| `flunk([msg])`                                                 | Ensures failure. This is useful to explicitly mark a test that isn't finished yet.|

The above are a subset of assertions that minitest supports. For an exhaustive
and more up-to-date list, please check the [minitest API
documentation](http://docs.seattlerb.org/minitest/Minitest), specifically
[`Minitest::Assertions`](http://docs.seattlerb.org/minitest/Minitest/Assertions.html).

With minitest you can add your own assertions. In fact, that's exactly what
Rails does. It includes some specialized assertions to make your life easier.

NOTE: Creating your own assertions is a topic that we won't cover in depth in
this guide.

### Rails-Specific Assertions

Rails adds some custom assertions of its own to the `minitest` framework:

| Assertion                                                                         | Purpose |
| --------------------------------------------------------------------------------- | ------- |
| [`assert_difference(expressions, difference = 1, message = nil) {...}`][] | Test numeric difference between the return value of an expression as a result of what is evaluated in the yielded block.|
| [`assert_no_difference(expressions, message = nil, &block)`][] | Asserts that the numeric result of evaluating an expression is not changed before and after invoking the passed in block.|
| [`assert_changes(expressions, message = nil, from:, to:, &block)`][] | Test that the result of evaluating an expression is changed after invoking the passed in block.|
| [`assert_no_changes(expressions, message = nil, &block)`][] | Test the result of evaluating an expression is not changed after invoking the passed in block.|
| [`assert_nothing_raised { block }`][] | Ensures that the given block doesn't raise any exceptions.|
| [`assert_recognizes(expected_options, path, extras = {}, message = nil)`][] | Asserts that the routing of the given path was handled correctly and that the parsed options (given in the expected_options hash) match path. Basically, it asserts that Rails recognizes the route given by expected_options.|
| [`assert_generates(expected_path, options, defaults = {}, extras = {}, message = nil)`][] | Asserts that the provided options can be used to generate the provided path. This is the inverse of assert_recognizes. The extra parameter is used to tell the request the names and values of additional request parameters that would be in a query string. The message parameter allows you to specify a custom error message for assertion failures.|
| [`assert_routing(expected_path, options, defaults = {}, extras = {}, message = nil)`][] | Asserts that `path` and `options` match both ways; in other words, it verifies that `path` generates `options` and then that `options` generates `path`. This essentially combines `assert_recognizes` and `assert_generates` into one step. The extras hash allows you to specify options that would normally be provided as a query string to the action. The message parameter allows you to specify a custom error message to display upon failure.|
| [`assert_response(type, message = nil)`][] | Asserts that the response comes with a specific status code. You can specify `:success` to indicate 200-299, `:redirect` to indicate 300-399, `:missing` to indicate 404, or `:error` to match the 500-599 range. You can also pass an explicit status number or its symbolic equivalent. For more information, see [full list of status codes](https://rubydoc.info/gems/rack/Rack/Utils#HTTP_STATUS_CODES-constant) and how their [mapping](https://rubydoc.info/gems/rack/Rack/Utils#SYMBOL_TO_STATUS_CODE-constant) works.|
| [`assert_redirected_to(options = {}, message = nil)`][] | Asserts that the response is a redirect to a URL matching the given options. You can also pass named routes such as `assert_redirected_to root_path` and Active Record objects such as `assert_redirected_to @article`.|
| [`assert_queries_count(count = nil, include_schema: false, &block)`][] | Asserts that `&block` generates an `int` number of SQL queries.|
| [`assert_no_queries(include_schema: false, &block)`][] | Asserts that `&block` generates no SQL queries.|
| [`assert_queries_match(pattern, count: nil, include_schema: false, &block)`][] | Asserts that `&block` generates SQL queries that match the pattern.|
| [`assert_no_queries_match(pattern, &block)`][] | Asserts that `&block` generates no SQL queries that match the pattern.|

[`assert_difference(expressions, difference = 1, message = nil) {...}`]: https://api.rubyonrails.org/classes/ActiveSupport/Testing/Assertions.html#method-i-assert_difference
[`assert_no_difference(expressions, message = nil, &block)`]: https://api.rubyonrails.org/classes/ActiveSupport/Testing/Assertions.html#method-i-assert_no_difference
[`assert_changes(expressions, message = nil, from:, to:, &block)`]: https://api.rubyonrails.org/classes/ActiveSupport/Testing/Assertions.html#method-i-assert_changes
[`assert_no_changes(expressions, message = nil, &block)`]: https://api.rubyonrails.org/classes/ActiveSupport/Testing/Assertions.html#method-i-assert_no_changes
[`assert_nothing_raised { block }`]: https://api.rubyonrails.org/classes/ActiveSupport/Testing/Assertions.html#method-i-assert_nothing_raised
[`assert_recognizes(expected_options, path, extras = {}, message = nil)`]: https://api.rubyonrails.org/classes/ActionDispatch/Assertions/RoutingAssertions.html#method-i-assert_recognizes
[`assert_generates(expected_path, options, defaults = {}, extras = {}, message = nil)`]: https://api.rubyonrails.org/classes/ActionDispatch/Assertions/RoutingAssertions.html#method-i-assert_generates
[`assert_routing(expected_path, options, defaults = {}, extras = {}, message = nil)`]: https://api.rubyonrails.org/classes/ActionDispatch/Assertions/RoutingAssertions.html#method-i-assert_routing
[`assert_response(type, message = nil)`]: https://api.rubyonrails.org/classes/ActionDispatch/Assertions/ResponseAssertions.html#method-i-assert_response
[`assert_redirected_to(options = {}, message = nil)`]: https://api.rubyonrails.org/classes/ActionDispatch/Assertions/ResponseAssertions.html#method-i-assert_redirected_to
[`assert_queries_count(count = nil, include_schema: false, &block)`]: https://api.rubyonrails.org/classes/ActiveRecord/Assertions/QueryAssertions.html#method-i-assert_queries_count
[`assert_no_queries(include_schema: false, &block)`]: https://api.rubyonrails.org/classes/ActiveRecord/Assertions/QueryAssertions.html#method-i-assert_no_queries
[`assert_queries_match(pattern, count: nil, include_schema: false, &block)`]: https://api.rubyonrails.org/classes/ActiveRecord/Assertions/QueryAssertions.html#method-i-assert_queries_match
[`assert_no_queries_match(pattern, &block)`]: https://api.rubyonrails.org/classes/ActiveRecord/Assertions/QueryAssertions.html#method-i-assert_no_queries_match

You'll see the usage of some of these assertions in the next chapter.

### Assertions in Test Cases

All the basic assertions such as `assert_equal` defined in
`Minitest::Assertions` are also available in the classes we use in our own test
cases. In fact, Rails provides the following classes for you to inherit from:

* [`ActiveSupport::TestCase`](https://api.rubyonrails.org/classes/ActiveSupport/TestCase.html)
* [`ActionMailer::TestCase`](https://api.rubyonrails.org/classes/ActionMailer/TestCase.html)
* [`ActionView::TestCase`](https://api.rubyonrails.org/classes/ActionView/TestCase.html)
* [`ActiveJob::TestCase`](https://api.rubyonrails.org/classes/ActiveJob/TestCase.html)
* [`ActionDispatch::Integration::Session`](https://api.rubyonrails.org/classes/ActionDispatch/Integration/Session.html)
* [`ActionDispatch::SystemTestCase`](https://api.rubyonrails.org/classes/ActionDispatch/SystemTestCase.html)
* [`Rails::Generators::TestCase`](https://api.rubyonrails.org/classes/Rails/Generators/TestCase.html)

Each of these classes include `Minitest::Assertions`, allowing us to use all of
the basic assertions in your tests.

TIP: For more information on `minitest`, refer to the [minitest
documentation](http://docs.seattlerb.org/minitest).

### The Rails Test Runner

We can run all of our tests at once by using the `bin/rails test` command.

Or we can run a single test file by appending the filename to the `bin/rails
test` command.

```bash
$ bin/rails test test/models/article_test.rb
Running 1 tests in a single process (parallelization threshold is 50)
Run options: --seed 1559

# Running:

..

Finished in 0.027034s, 73.9810 runs/s, 110.9715 assertions/s.

2 runs, 3 assertions, 0 failures, 0 errors, 0 skips
```

This will run all test methods from the test case.

You can also run a particular test method from the test case by providing the
`-n` or `--name` flag and the test's method name.

```bash
$ bin/rails test test/models/article_test.rb -n test_the_truth
Running 1 tests in a single process (parallelization threshold is 50)
Run options: -n test_the_truth --seed 43583

# Running:

.

Finished tests in 0.009064s, 110.3266 tests/s, 110.3266 assertions/s.

1 tests, 1 assertions, 0 failures, 0 errors, 0 skips
```

You can also run a test at a specific line by providing the line number.

```bash
$ bin/rails test test/models/article_test.rb:6 # run specific test and line
```

You can also run a range of tests by providing the line range.

```bash
$ bin/rails test test/models/article_test.rb:6-20 # runs tests from line 6 to 20
```

You can also run an entire directory of tests by providing the path to the
directory.

```bash
$ bin/rails test test/controllers # run all tests from specific directory
```

The test runner also provides a lot of other features like failing fast, showing
verbose progress, and so on. Check the documentation of the test runner using
the command below:

```bash
$ bin/rails test -h
Usage:
  bin/rails test [PATHS...]

Run tests except system tests

Examples:
    You can run a single test by appending a line number to a filename:

        bin/rails test test/models/user_test.rb:27

    You can run multiple tests with in a line range by appending the line range to a filename:

        bin/rails test test/models/user_test.rb:10-20

    You can run multiple files and directories at the same time:

        bin/rails test test/controllers test/integration/login_test.rb

    By default test failures and errors are reported inline during a run.

minitest options:
    -h, --help                       Display this help.
        --no-plugins                 Bypass minitest plugin auto-loading (or set $MT_NO_PLUGINS).
    -s, --seed SEED                  Sets random seed. Also via env. Eg: SEED=n rake
    -v, --verbose                    Verbose. Show progress processing files.
        --show-skips                 Show skipped at the end of run.
    -n, --name PATTERN               Filter run on /regexp/ or string.
        --exclude PATTERN            Exclude /regexp/ or string from run.
    -S, --skip CODES                 Skip reporting of certain types of results (eg E).

Known extensions: rails, pride
    -w, --warnings                   Run with Ruby warnings enabled
    -e, --environment ENV            Run tests in the ENV environment
    -b, --backtrace                  Show the complete backtrace
    -d, --defer-output               Output test failures and errors after the test run
    -f, --fail-fast                  Abort test run on first failure or error
    -c, --[no-]color                 Enable color in the output
        --profile [COUNT]            Enable profiling of tests and list the slowest test cases (default: 10)
    -p, --pride                      Pride. Show your testing pride!
```

The Test Database
-----------------

Just about every Rails application interacts heavily with a database and so your
tests will need a database to interact with as well. This section covers how to
set up this test database and populate it with sample data.

As mentioned in the [Test Environment section](#the-test-environment), every
Rails application has three environments: development, test, and production. The
database for each one of them is configured in `config/database.yml`.

A dedicated test database allows you to set up and interact with test data in
isolation. This way your tests can interact with test data with confidence,
without worrying about the data in the development or production databases.

### Maintaining the Test Database Schema

In order to run your tests, your test database needs the current schema. The
test helper checks whether your test database has any pending migrations. It
will try to load your `db/schema.rb` or `db/structure.sql` into the test
database. If migrations are still pending, an error will be raised. Usually this
indicates that your schema is not fully migrated. Running the migrations (using
`bin/rails db:migrate RAILS_ENV=test`) will bring the schema up to date.

NOTE: If there were modifications to existing migrations, the test database
needs to be rebuilt. This can be done by executing `bin/rails test:db`.

### Fixtures

For good tests, you'll need to give some thought to setting up test data. In
Rails, you can handle this by defining and customizing fixtures. You can find
comprehensive documentation in the [Fixtures API
documentation](https://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html).

#### What are Fixtures?

_Fixtures_ is a fancy word for a consistent set of test data. Fixtures allow you to populate your
testing database with predefined data before your tests run. Fixtures are
database independent and written in YAML. There is one file per model.

NOTE: Fixtures are not designed to create every object that your tests need, and
are best managed when only used for default data that can be applied to the
common case.

Fixtures are stored in your `test/fixtures` directory.

#### YAML

[YAML](https://en.wikipedia.org/wiki/YAML) is a human-readable data serialization language.
YAML-formatted fixtures are a human-friendly way to describe your sample data.
These types of fixtures have the **.yml** file extension (as in `users.yml`).

Here's a sample YAML fixture file:

```yaml
# lo & behold! I am a YAML comment!
david:
  name: David Heinemeier Hansson
  birthday: 1979-10-15
  profession: Systems development

steve:
  name: Steve Ross Kellock
  birthday: 1974-09-27
  profession: guy with keyboard
```

Each fixture is given a name followed by an indented list of colon-separated
key/value pairs. Records are typically separated by a blank line. You can place
comments in a fixture file by using the # character in the first column.

If you are working with [associations](association_basics.html), you can define
a reference node between two different fixtures. Here's an example with a
`belongs_to`/`has_many` association:

```yaml
# test/fixtures/categories.yml
web_frameworks:
  name: Web Frameworks
```

```yaml
# test/fixtures/articles.yml
first:
  title: Welcome to Rails!
  category: web_frameworks
```

```yaml
# test/fixtures/action_text/rich_texts.yml
first_content:
  record: first (Article)
  name: content
  body: <div>Hello, from <strong>a fixture</strong></div>
```

Notice the `category` key of the `first` Article found in
`fixtures/articles.yml` has a value of `web_frameworks`, and that the `record` key of the
`first_content` entry found in `fixtures/action_text/rich_texts.yml` has a value
of `first (Article)`. This hints to Active Record to load the Category `web_frameworks`
found in `fixtures/categories.yml` for the former, and Action Text to load the
Article `first` found in `fixtures/articles.yml` for the latter.

NOTE: For associations to reference one another by name, you can use the fixture
name instead of specifying the `id:` attribute on the associated fixtures. Rails
will auto-assign a primary key to be consistent between runs. For more
information on this association behavior please read the [Fixtures API
documentation](https://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html).

#### File Attachment Fixtures

Like other Active Record-backed models, Active Storage attachment records
inherit from ActiveRecord::Base instances and can therefore be populated by
fixtures.

Consider an `Article` model that has an associated image as a `thumbnail`
attachment, along with fixture data YAML:

```ruby
class Article < ApplicationRecord
  has_one_attached :thumbnail
end
```

```yaml
# test/fixtures/articles.yml
first:
  title: An Article
```

Assuming that there is an [image/png][] encoded file at
`test/fixtures/files/first.png`, the following YAML fixture entries will
generate the related `ActiveStorage::Blob` and `ActiveStorage::Attachment`
records:

```yaml
# test/fixtures/active_storage/blobs.yml
first_thumbnail_blob: <%= ActiveStorage::FixtureSet.blob filename: "first.png" %>
```

```yaml
# test/fixtures/active_storage/attachments.yml
first_thumbnail_attachment:
  name: thumbnail
  record: first (Article)
  blob: first_thumbnail_blob
```

[image/png]:
    https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types#image_types

#### Embedding Code in Fixtures

ERB allows you to embed Ruby code within templates. The YAML fixture format is
pre-processed with ERB when Rails loads fixtures. This allows you to use Ruby to
help you generate some sample data. For example, the following code generates a
thousand users:

```erb
<% 1000.times do |n| %>
  user_<%= n %>:
    username: <%= "user#{n}" %>
    email: <%= "user#{n}@example.com" %>
<% end %>
```

#### Fixtures in Action

Rails automatically loads all fixtures from the `test/fixtures` directory by
default. Loading involves three steps:

1. Remove any existing data from the table corresponding to the fixture
2. Load the fixture data into the table
3. Dump the fixture data into a method in case you want to access it directly

TIP: In order to remove existing data from the database, Rails tries to disable
referential integrity triggers (like foreign keys and check constraints). If you
are getting permission errors on running tests, make sure the database user has
the permission to disable these triggers in the testing environment. (In
PostgreSQL, only superusers can disable all triggers. Read more about
[permissions in the PostgreSQL
docs](https://www.postgresql.org/docs/current/sql-altertable.html)).

#### Fixtures are Active Record Objects

Fixtures are instances of Active Record. As mentioned above, you can access the
object directly because it is automatically available as a method whose scope is
local to the test case. For example:

```ruby
# this will return the User object for the fixture named david
users(:david)

# this will return the property for david called id
users(:david).id

# methods available to the User object can also be accessed
david = users(:david)
david.call(david.partner)
```

To get multiple fixtures at once, you can pass in a list of fixture names. For
example:

```ruby
# this will return an array containing the fixtures david and steve
users(:david, :steve)
```

### Transactions

By default, Rails automatically wraps tests in a database transaction that is
rolled back once completed. This makes tests independent of each other and means
that changes to the database are only visible within a single test.

```ruby
class MyTest < ActiveSupport::TestCase
  test "newly created users are active by default" do
    # Since the test is implicitly wrapped in a database transaction, the user
    # created here won't be seen by other tests.
    assert User.create.active?
  end
end
```

The method
[`ActiveRecord::Base.current_transaction`](https://api.rubyonrails.org/classes/ActiveRecord/Transactions/ClassMethods.html#method-i-current_transaction)
still acts as intended, though:

```ruby
class MyTest < ActiveSupport::TestCase
  test "Active Record current_transaction method works as expected" do
    # The implicit transaction around tests does not interfere with the
    # application-level semantics of the current_transaction.
    assert User.current_transaction.blank?
  end
end
```

If there are [multiple writing databases](active_record_multiple_databases.html)
in place, tests are wrapped in as many respective transactions, and all of them
are rolled back.

#### Opting-out of Test Transactions

Individual test cases can opt-out:

```ruby
class MyTest < ActiveSupport::TestCase
  # No implicit database transaction wraps the tests in this test case.
  self.use_transactional_tests = false
end
```

Testing Models
--------------

Model tests are used to test the models of your application and their associated
logic. You can test this logic using the assertions and fixtures that we've
explored in the sections above.

Rails model tests are stored under the `test/models` directory. Rails provides a
generator to create a model test skeleton for you.

```bash
$ bin/rails generate test_unit:model article
create  test/models/article_test.rb
```

This command will generate the following file:

```ruby
# article_test.rb
require "test_helper"

class ArticleTest < ActiveSupport::TestCase
  # test "the truth" do
  #   assert true
  # end
end
```

Model tests don't have their own superclass like `ActionMailer::TestCase`.
Instead, they inherit from
[`ActiveSupport::TestCase`](https://api.rubyonrails.org/classes/ActiveSupport/TestCase.html).

Functional Testing for Controllers
----------------------------------

When writing functional tests, you are focusing on testing how controller
actions handle the requests and the expected result or response. Functional
controller tests are sometimes used in cases where system tests are not
appropriate, e.g., to confirm an API response.

### What to Include in Your Functional Tests

You could test for things such as:

* was the web request successful?
* was the user redirected to the right page?
* was the user successfully authenticated?
* was the correct information displayed in the response?

The easiest way to see functional tests in action is to generate a controller
using the scaffold generator:

```bash
$ bin/rails generate scaffold_controller article
...
create  app/controllers/articles_controller.rb
...
invoke  test_unit
create    test/controllers/articles_controller_test.rb
...
```

This will generate the controller code and tests for an `Article` resource. You
can take a look at the file `articles_controller_test.rb` in the
`test/controllers` directory.

If you already have a controller and just want to generate the test scaffold
code for each of the seven default actions, you can use the following command:

```bash
$ bin/rails generate test_unit:scaffold article
...
invoke  test_unit
create    test/controllers/articles_controller_test.rb
...
```

NOTE: if you are generating test scaffold code, you will see an `@article` value
is set and used throughout the test file. This instance of `article` uses the
attributes nested within a `:one` key in the `test/fixtures/articles.yml` file.
Make sure you have set the key and related values in this file before you try to
run the tests.

Let's take a look at one such test, `test_should_get_index` from the file
`articles_controller_test.rb`.

```ruby
# articles_controller_test.rb
class ArticlesControllerTest < ActionDispatch::IntegrationTest
  test "should get index" do
    get articles_url
    assert_response :success
  end
end
```

In the `test_should_get_index` test, Rails simulates a request on the action
called `index`, making sure the request was successful, and also ensuring that
the right response body has been generated.

The `get` method kicks off the web request and populates the results into the
`@response`. It can accept up to 6 arguments:

* The URI of the controller action you are requesting. This can be in the form
  of a string or a route helper (e.g. `articles_url`).
* `params`: option with a hash of request parameters to pass into the action
  (e.g. query string parameters or article variables).
* `headers`: for setting the headers that will be passed with the request.
* `env`: for customizing the request environment as needed.
* `xhr`: whether the request is AJAX request or not. Can be set to true for
  marking the request as AJAX.
* `as`: for encoding the request with different content type.

All of these keyword arguments are optional.

Example: Calling the `:show` action (via a `get` request) for the first
`Article`, passing in an `HTTP_REFERER` header:

```ruby
get article_url(Article.first), headers: { "HTTP_REFERER" => "http://example.com/home" }
```

Another example: Calling the `:update` action (via a `patch` request) for the
last `Article`, passing in new text for the `title` in `params`, as an AJAX
request:

```ruby
patch article_url(Article.last), params: { article: { title: "updated" } }, xhr: true
```

One more example: Calling the `:create` action (via a `post` request) to create
a new article, passing in text for the `title` in `params`, as JSON request:

```ruby
post articles_url, params: { article: { title: "Ahoy!" } }, as: :json
```

NOTE: If you try running the `test_should_create_article` test from
`articles_controller_test.rb` it will (correctly) fail due to the newly added
model-level validation.

Now to modify the `test_should_create_article` test in
`articles_controller_test.rb` so that this test passes:

```ruby
test "should create article" do
  assert_difference("Article.count") do
    post articles_url, params: { article: { body: "Rails is awesome!", title: "Hello Rails" } }
  end

  assert_redirected_to article_path(Article.last)
end
```

You can now run this test and it will pass.

NOTE: If you followed the steps in the [Basic
Authentication](getting_started.html#adding-authentication) section, you'll need
to add authorization to every request header to get all the tests passing:

```ruby
post articles_url, params: { article: { body: "Rails is awesome!", title: "Hello Rails" } }, headers: { Authorization: ActionController::HttpAuthentication::Basic.encode_credentials("dhh", "secret") }
```

### HTTP Request Types for Functional Tests

If you're familiar with the HTTP protocol, you'll know that `get` is a type of
request. There are 6 request types supported in Rails functional tests:

* `get`
* `post`
* `patch`
* `put`
* `head`
* `delete`

All of the request types have equivalent methods that you can use. In a typical
CRUD application you'll be using `post`, `get`, `put`, and `delete` most
often.

NOTE: Functional tests do not verify whether the specified request type is
accepted by the action; instead, they focus on the result. For testing the
request type, request tests are available, making your tests more purposeful.

### Testing XHR (AJAX) Requests

An AJAX request (Asynchronous JavaScript and XML) is a technique where content is
fetched from the server using asynchronous HTTP requests and the relevant parts
of the page are updated without requiring a full page load.

To test AJAX requests, you can specify the `xhr: true` option to `get`, `post`,
`patch`, `put`, and `delete` methods. For example:

```ruby
test "AJAX request" do
  article = articles(:one)
  get article_url(article), xhr: true

  assert_equal "hello world", @response.body
  assert_equal "text/javascript", @response.media_type
end
```

### Testing Other Request Objects

After any request has been made and processed, you will have 3 Hash objects
ready for use:

* `cookies` - Any cookies that are set
* `flash` - Any objects living in the flash
* `session` - Any object living in session variables

As is the case with normal Hash objects, you can access the values by
referencing the keys by string. You can also reference them by symbol name. For
example:

```ruby
flash["gordon"]               # or flash[:gordon]
session["shmession"]          # or session[:shmession]
cookies["are_good_for_u"]     # or cookies[:are_good_for_u]
```

### Instance Variables

You also have access to three instance variables in your functional tests after
a request is made:

* `@controller` - The controller processing the request
* `@request` - The request object
* `@response` - The response object

```ruby
class ArticlesControllerTest < ActionDispatch::IntegrationTest
  test "should get index" do
    get articles_url

    assert_equal "index", @controller.action_name
    assert_equal "application/x-www-form-urlencoded", @request.media_type
    assert_match "Articles", @response.body
  end
end
```

### Setting Headers and CGI Variables

HTTP headers are pieces of information sent along with HTTP requests to provide
important metadata. CGI variables are environment variables used to exchange
information between the web server and the application.

HTTP headers and CGI variables can be tested by being passed as headers:

```ruby
# setting an HTTP Header
get articles_url, headers: { "Content-Type": "text/plain" } # simulate the request with custom header

# setting a CGI variable
get articles_url, headers: { "HTTP_REFERER": "http://example.com/home" } # simulate the request with custom env variable
```

### Testing `flash` Notices

As can be seen in the [testing other request objects
section](#testing-other-request-objects), one of the three hash objects that is
accessible in the tests is `flash`. This section outlines how to test the
appearance of a `flash` message in our blog application whenever someone
successfully creates a new article.

First, an assertion should be added to the `test_should_create_article` test:

```ruby
test "should create article" do
  assert_difference("Article.count") do
    post articles_url, params: { article: { title: "Some title" } }
  end

  assert_redirected_to article_path(Article.last)
  assert_equal "Article was successfully created.", flash[:notice]
end
```

If the test is run now, it should fail:

```bash
$ bin/rails test test/controllers/articles_controller_test.rb -n test_should_create_article
Running 1 tests in a single process (parallelization threshold is 50)
Run options: -n test_should_create_article --seed 32266

# Running:

F

Finished in 0.114870s, 8.7055 runs/s, 34.8220 assertions/s.

  1) Failure:
ArticlesControllerTest#test_should_create_article [/test/controllers/articles_controller_test.rb:16]:
--- expected
+++ actual
@@ -1 +1 @@
-"Article was successfully created."
+nil

1 runs, 4 assertions, 1 failures, 0 errors, 0 skips
```

Now implement the flash message in the controller. The `:create` action should
look like this:

```ruby
def create
  @article = Article.new(article_params)

  if @article.save
    flash[:notice] = "Article was successfully created."
    redirect_to @article
  else
    render "new"
  end
end
```

Now, if the tests are run they should pass:

```bash
$ bin/rails test test/controllers/articles_controller_test.rb -n test_should_create_article
Running 1 tests in a single process (parallelization threshold is 50)
Run options: -n test_should_create_article --seed 18981

# Running:

.

Finished in 0.081972s, 12.1993 runs/s, 48.7972 assertions/s.

1 runs, 4 assertions, 0 failures, 0 errors, 0 skips
```

NOTE: If you generated your controller using the scaffold generator, the flash
message will already be implemented in your `create` action.

### Tests for `show`, `update`, and `delete` Actions

So far in the guide tests for the `:index` as well as the`:create` action have
been outlined. What about the other actions?

You can write a test for `:show` as follows:

```ruby
test "should show article" do
  article = articles(:one)
  get article_url(article)
  assert_response :success
end
```

If you remember from our discussion earlier on [fixtures](#fixtures), the
`articles()` method will provide access to the articles fixtures.

How about deleting an existing article?

```ruby
test "should delete article" do
  article = articles(:one)
  assert_difference("Article.count", -1) do
    delete article_url(article)
  end

  assert_redirected_to articles_path
end
```

Here is a test for updating an existing article:

```ruby
test "should update article" do
  article = articles(:one)

  patch article_url(article), params: { article: { title: "updated" } }

  assert_redirected_to article_path(article)
  # Reload article to refresh data and assert that title is updated.
  article.reload
  assert_equal "updated", article.title
end
```

Notice that there is some duplication in these three tests - they both access
the same article fixture data. It is possible to DRY ('Don't Repeat
Yourself') the implementation by using the `setup` and `teardown` methods
provided by `ActiveSupport::Callbacks`.

The tests might look like this:

```ruby
require "test_helper"

class ArticlesControllerTest < ActionDispatch::IntegrationTest
  # called before every single test
  setup do
    @article = articles(:one)
  end

  # called after every single test
  teardown do
    # when controller is using cache it may be a good idea to reset it afterwards
    Rails.cache.clear
  end

  test "should show article" do
    # Reuse the @article instance variable from setup
    get article_url(@article)
    assert_response :success
  end

  test "should destroy article" do
    assert_difference("Article.count", -1) do
      delete article_url(@article)
    end

    assert_redirected_to articles_path
  end

  test "should update article" do
    patch article_url(@article), params: { article: { title: "updated" } }

    assert_redirected_to article_path(@article)
    # Reload association to fetch updated data and assert that title is updated.
    @article.reload
    assert_equal "updated", @article.title
  end
end
```

NOTE: Similar to other callbacks in Rails, the `setup` and `teardown` methods
can also accept a block, lambda, or a method name as a symbol to be called.

Integration Testing
-------------------

Integration tests take functional controller tests one step further - they focus
on testing how several parts of an application interact, and are generally used
to test important workflows. Rails integration tests are stored in the
`test/integration` directory.

Rails provides a generator to create an integration test skeleton as follows:

```bash
$ bin/rails generate integration_test user_flows
      invoke  test_unit
      create  test/integration/user_flows_test.rb
```

Here's what a freshly generated integration test looks like:

```ruby
require "test_helper"

class UserFlowsTest < ActionDispatch::IntegrationTest
  # test "the truth" do
  #   assert true
  # end
end
```

Here the test is inheriting from
[`ActionDispatch::IntegrationTest`](https://api.rubyonrails.org/classes/ActionDispatch/IntegrationTest.html).
This makes some additional [helpers available for integration
tests](testing.html#helpers-available-for-integration-tests) alongside the
standard testing helpers.

### Implementing an Integration Test

Let's add an integration test to our blog application, by starting with a basic
workflow of creating a new blog article to verify that everything is working
properly.

Start by generating the integration test skeleton:

```bash
$ bin/rails generate integration_test blog_flow
```

It should have created a test file placeholder. With the output of the previous
command you should see:

```
      invoke  test_unit
      create    test/integration/blog_flow_test.rb
```

Now open that file and write the first assertion:

```ruby
require "test_helper"

class BlogFlowTest < ActionDispatch::IntegrationTest
  test "can see the welcome page" do
    get "/"
    assert_dom "h1", "Welcome#index"
  end
end
```

If you visit the root path, you should see `welcome/index.html.erb` rendered for
the view. So this assertion should pass.

NOTE: The assertion `assert_dom` (aliased to `assert_select`) is available in integration tests to check
the presence of key HTML elements and their content.

#### Creating Articles Integration

To test the ability to create a new article in our blog and display the
resulting article, see the example below:

```ruby
test "can create an article" do
  get "/articles/new"
  assert_response :success

  post "/articles",
    params: { article: { title: "can create", body: "article successfully." } }
  assert_response :redirect
  follow_redirect!
  assert_response :success
  assert_dom "p", "Title:\n  can create"
end
```

The `:new` action of our Articles controller is called first, and the response
should be successful.

Next, a `post` request is made to the `:create` action of the Articles
controller:

```ruby
post "/articles",
  params: { article: { title: "can create", body: "article successfully." } }
assert_response :redirect
follow_redirect!
```

The two lines following the request are to handle the redirect setup when
creating a new article.

NOTE: Don't forget to call `follow_redirect!` if you plan to make subsequent
requests after a redirect is made.

Finally it can be asserted that the response was successful and the
newly-created article is readable on the page.

A very small workflow for visiting our blog and creating a new article was
successfully tested above. To extend this, additional tests could be added for
features like adding comments, editing comments or removing articles.
Integration tests are a great place to experiment with all kinds of use cases
for our applications.

### Helpers Available for Integration Tests

There are numerous helpers to choose from for use in integration tests. Some
include:

* [`ActionDispatch::Integration::Runner`](https://api.rubyonrails.org/classes/ActionDispatch/Integration/Runner.html)
  for helpers relating to the integration test runner, including creating a new
  session.

* [`ActionDispatch::Integration::RequestHelpers`](https://api.rubyonrails.org/classes/ActionDispatch/Integration/RequestHelpers.html)
  for performing requests.

* [`ActionDispatch::TestProcess::FixtureFile`](https://api.rubyonrails.org/classes/ActionDispatch/TestProcess/FixtureFile.html)
  for uploading files.

* [`ActionDispatch::Integration::Session`](https://api.rubyonrails.org/classes/ActionDispatch/Integration/Session.html)
  to modify sessions or the state of the integration tests.

System Testing
--------------

Similarly to integration testing, system testing allows you to test how the
components of your app work together, but from the point of view of a user. It
does this by running tests in either a real or a headless browser (a browser
which runs in the background without opening a visible window). System tests use
[Capybara](https://www.rubydoc.info/github/jnicklas/capybara) under the hood.

Rails system tests are stored in the `test/system` directory in your
application. To generate a system test skeleton, run the following command:

```bash
$ bin/rails generate system_test users
      invoke test_unit
      create test/system/users_test.rb
```

Here's what a freshly generated system test looks like:

```ruby
require "application_system_test_case"

class UsersTest < ApplicationSystemTestCase
  # test "visiting the index" do
  #   visit users_url
  #
  #   assert_dom "h1", text: "Users"
  # end
end
```

By default, system tests are run with the Selenium driver, using the Chrome
browser, and a screen size of 1400x1400. The next section explains how to change
the default settings.

### Changing the Default Settings

Rails makes changing the default settings for system tests very simple. All the
setup is abstracted away so you can focus on writing your tests.

When you generate a new application or scaffold, an
`application_system_test_case.rb` file is created in the test directory. This is
where all the configuration for your system tests should live.

If you want to change the default settings, you can change what the system tests
are "driven by". If you want to change the driver from Selenium to Cuprite,
you'd add the [`cuprite`](https://github.com/rubycdp/cuprite) gem to your
`Gemfile`. Then in your `application_system_test_case.rb` file you'd do the
following:

```ruby
require "test_helper"
require "capybara/cuprite"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :cuprite
end
```

The driver name is a required argument for `driven_by`. The optional arguments
that can be passed to `driven_by` are `:using` for the browser (this will only
be used by Selenium), `:screen_size` to change the size of the screen for
screenshots, and `:options` which can be used to set options supported by the
driver.

```ruby
require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :firefox
end
```

If you want to use a headless browser, you could use Headless Chrome or Headless
Firefox by adding `headless_chrome` or `headless_firefox` in the `:using`
argument.

```ruby
require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :headless_chrome
end
```

If you want to use a remote browser, e.g. [Headless Chrome in
Docker](https://github.com/SeleniumHQ/docker-selenium), you have to add a remote
`url` and set `browser` as remote through `options`.

```ruby
require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  url = ENV.fetch("SELENIUM_REMOTE_URL", nil)
  options = if url
    { browser: :remote, url: url }
  else
    { browser: :chrome }
  end
  driven_by :selenium, using: :headless_chrome, options: options
end
```

Now you should get a connection to the remote browser.

```bash
$ SELENIUM_REMOTE_URL=http://localhost:4444/wd/hub bin/rails test:system
```

If your application is remote, e.g. within a Docker container, Capybara needs
more input about how to [call remote
servers](https://github.com/teamcapybara/capybara#calling-remote-servers).

```ruby
require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  setup do
      Capybara.server_host = "0.0.0.0" # bind to all interfaces
      Capybara.app_host = "http://#{IPSocket.getaddress(Socket.gethostname)}" if ENV["SELENIUM_REMOTE_URL"].present?
    end
  # ...
end
```

Now you should get a connection to a remote browser and server, regardless if it
is running in a Docker container or CI.

If your Capybara configuration requires more setup than provided by Rails, this
additional configuration can be added into the `application_system_test_case.rb`
file.

Please see [Capybara's
documentation](https://github.com/teamcapybara/capybara#setup) for additional
settings.

### Implementing a System Test

This section will demonstrate how to add a system test to your application,
which tests a visit to the index page to create a new blog article.

If you used the scaffold generator, a system test skeleton was automatically
created for you. If you didn't use the scaffold generator, start by creating a
system test skeleton.

```bash
$ bin/rails generate system_test articles
```

It should have created a test file placeholder. With the output of the previous
command you should see:

```
      invoke  test_unit
      create    test/system/articles_test.rb
```

Now, let's open that file and write the first assertion:

```ruby
require "application_system_test_case"

class ArticlesTest < ApplicationSystemTestCase
  test "viewing the index" do
    visit articles_path
    assert_selector "h1", text: "Articles"
  end
end
```

The test should see that there is an `h1` on the articles index page and pass.

Run the system tests.

```bash
$ bin/rails test:system
```

NOTE: By default, running `bin/rails test` won't run your system tests. Make
sure to run `bin/rails test:system` to actually run them. You can also run
`bin/rails test:all` to run all tests, including system tests.

#### Creating Articles System Test

Now you can test the flow for creating a new article.

```ruby
test "should create Article" do
  visit articles_path

  click_on "New Article"

  fill_in "Title", with: "Creating an Article"
  fill_in "Body", with: "Created this article successfully!"

  click_on "Create Article"

  assert_text "Creating an Article"
end
```

The first step is to call `visit articles_path`. This will take the test to the
articles index page.

Then the `click_on "New Article"` will find the "New Article" button on the
index page. This will redirect the browser to `/articles/new`.

Then the test will fill in the title and body of the article with the specified
text. Once the fields are filled in, "Create Article" is clicked on which will
send a POST request to `/articles/create`.

This redirects the user back to the articles index page, and there it is
asserted that the text from the new article's title is on the articles index
page.

#### Testing for Multiple Screen Sizes

If you want to test for mobile sizes in addition to testing for desktop, you can
create another class that inherits from `ActionDispatch::SystemTestCase` and use
it in your test suite. In this example, a file called
`mobile_system_test_case.rb` is created in the `/test` directory with the
following configuration.

```ruby
require "test_helper"

class MobileSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :chrome, screen_size: [375, 667]
end
```

To use this configuration, create a test inside `test/system` that inherits from
`MobileSystemTestCase`. Now you can test your app using multiple different
configurations.

```ruby
require "mobile_system_test_case"

class PostsTest < MobileSystemTestCase
  test "visiting the index" do
    visit posts_url
    assert_selector "h1", text: "Posts"
  end
end
```

#### Capybara Assertions

Here's an extract of the assertions provided by
[`Capybara`](https://rubydoc.info/github/teamcapybara/capybara/master/Capybara/Minitest/Assertions)
which can be used in system tests.

| Assertion                                                        | Purpose |
| ---------------------------------------------------------------- | ------- |
| `assert_button(locator = nil, **options, &optional_filter_block)`| Checks if the page has a button with the given text, value or id. |
| `assert_current_path(string, **options)`                         | Asserts that the page has the given path. |
| `assert_field(locator = nil, **options, &optional_filter_block)` | Checks if the page has a form field with the given label, name or id. |
| `assert_link(locator = nil, **options, &optional_filter_block)`  | Checks if the page has a link with the given text or id. |
| `assert_selector(*args, &optional_filter_block)`                 | Asserts that a given selector is on the page. |
| `assert_table(locator = nil, **options, &optional_filter_block`  | Checks if the page has a table with the given id or caption. |
| `assert_text(type, text, **options)`                             | Asserts that the page has the given text content. |


#### Screenshot Helper

The
[`ScreenshotHelper`](https://api.rubyonrails.org/classes/ActionDispatch/SystemTesting/TestHelpers/ScreenshotHelper.html)
is a helper designed to capture screenshots of your tests. This can be helpful
for viewing the browser at the point a test failed, or to view screenshots later
for debugging.

Two methods are provided: `take_screenshot` and `take_failed_screenshot`.
`take_failed_screenshot` is automatically included in `before_teardown` inside
Rails.

The `take_screenshot` helper method can be included anywhere in your tests to
take a screenshot of the browser.

#### Taking It Further

System testing is similar to [integration testing](#integration-testing) in that
it tests the user's interaction with your controller, model, and view, but
system testing tests your application as if a real user were using it. With
system tests, you can test anything that a user would do in your application
such as commenting, deleting articles, publishing draft articles, etc.

Test Helpers
------------

To avoid code duplication, you can add your own test helpers. Here is an example
for signing in:

```ruby
# test/test_helper.rb

module SignInHelper
  def sign_in_as(user)
    post sign_in_url(email: user.email, password: user.password)
  end
end

class ActionDispatch::IntegrationTest
  include SignInHelper
end
```

```ruby
require "test_helper"

class ProfileControllerTest < ActionDispatch::IntegrationTest
  test "should show profile" do
    # helper is now reusable from any controller test case
    sign_in_as users(:david)

    get profile_url
    assert_response :success
  end
end
```

### Using Separate Files

If you find your helpers are cluttering `test_helper.rb`, you can extract them
into separate files. A good place to store them is `test/lib` or
`test/test_helpers`.

```ruby
# test/test_helpers/multiple_assertions.rb
module MultipleAssertions
  def assert_multiple_of_forty_two(number)
    assert (number % 42 == 0), "expected #{number} to be a multiple of 42"
  end
end
```

These helpers can then be explicitly required and included as needed:

```ruby
require "test_helper"
require "test_helpers/multiple_assertions"

class NumberTest < ActiveSupport::TestCase
  include MultipleAssertions

  test "420 is a multiple of 42" do
    assert_multiple_of_forty_two 420
  end
end
```

They can also continue to be included directly into the relevant parent classes:

```ruby
# test/test_helper.rb
require "test_helpers/sign_in_helper"

class ActionDispatch::IntegrationTest
  include SignInHelper
end
```

### Eagerly Requiring Helpers

You may find it convenient to eagerly require helpers in `test_helper.rb` so
your test files have implicit access to them. This can be accomplished using
globbing, as follows

```ruby
# test/test_helper.rb
Dir[Rails.root.join("test", "test_helpers", "**", "*.rb")].each { |file| require file }
```

This has the downside of increasing the boot-up time, as opposed to manually
requiring only the necessary files in your individual tests.

Testing Routes
--------------

Like everything else in your Rails application, you can test your routes. Route
tests are stored in `test/controllers/` or are part of controller tests. If your
application has complex routes, Rails provides a number of useful helpers to
test them.

For more information on routing assertions available in Rails, see the API
documentation for
[`ActionDispatch::Assertions::RoutingAssertions`](https://api.rubyonrails.org/classes/ActionDispatch/Assertions/RoutingAssertions.html).

Testing Views
-------------

Testing the response to your request by asserting the presence of key HTML
elements and their content is one way to test the views of your application.
Like route tests, view tests are stored in `test/controllers/` or are part of
controller tests.

### Querying the HTML

Methods like `assert_dom` and `assert_dom_equal` allow you to query HTML
elements of the response by using a simple yet powerful syntax.

`assert_dom` is an assertion that will return true if matching elements are
found. For example, you could verify that the page title is "Welcome to the
Rails Testing Guide" as follows:

```ruby
assert_dom "title", "Welcome to the Rails Testing Guide"
```

You can also use nested `assert_dom` blocks for deeper investigation.

In the following example, the inner `assert_dom` for `li.menu_item` runs within
the collection of elements selected by the outer block:

```ruby
assert_dom "ul.navigation" do
  assert_dom "li.menu_item"
end
```

A collection of selected elements may also be iterated through so that
`assert_dom` may be called separately for each element. For example, if the
response contains two ordered lists, each with four nested list elements then
the following tests will both pass.

```ruby
assert_dom "ol" do |elements|
  elements.each do |element|
    assert_dom element, "li", 4
  end
end

assert_dom "ol" do
  assert_dom "li", 8
end
```

The `assert_dom_equal` method compares two HTML strings to see if they are
equal:

```ruby
assert_dom_equal '<a href="http://www.further-reading.com">Read more</a>',
  link_to("Read more", "http://www.further-reading.com")
```

For more advanced usage, refer to the [`rails-dom-testing`
documentation](https://github.com/rails/rails-dom-testing).

In order to integrate with [rails-dom-testing][], tests that inherit from
`ActionView::TestCase` declare a `document_root_element` method that returns the
rendered content as an instance of a
[Nokogiri::XML::Node](https://nokogiri.org/rdoc/Nokogiri/XML/Node.html):

```ruby
test "renders a link to itself" do
  article = Article.create! title: "Hello, world"

  render "articles/article", article: article
  anchor = document_root_element.at("a")

  assert_equal article.name, anchor.text
  assert_equal article_url(article), anchor["href"]
end
```

If your application depends on [Nokogiri >=
1.14.0](https://github.com/sparklemotion/nokogiri/releases/tag/v1.14.0) or
higher, and [minitest >=
5.18.0](https://github.com/minitest/minitest/blob/v5.18.0/History.rdoc#5180--2023-03-04-),
`document_root_element` supports [Ruby's Pattern
Matching](https://docs.ruby-lang.org/en/master/syntax/pattern_matching_rdoc.html):

```ruby
test "renders a link to itself" do
  article = Article.create! title: "Hello, world"

  render "articles/article", article: article
  anchor = document_root_element.at("a")
  url = article_url(article)

  assert_pattern do
    anchor => { content: "Hello, world", attributes: [{ name: "href", value: url }] }
  end
end
```

If you'd like to access the same [Capybara-powered
Assertions](https://rubydoc.info/github/teamcapybara/capybara/master/Capybara/Minitest/Assertions)
that your [System Testing](#system-testing) tests utilize, you can define a base
class that inherits from `ActionView::TestCase` and transforms the
`document_root_element` into a `page` method:

```ruby
# test/view_partial_test_case.rb

require "test_helper"
require "capybara/minitest"

class ViewPartialTestCase < ActionView::TestCase
  include Capybara::Minitest::Assertions

  def page
    Capybara.string(rendered)
  end
end

# test/views/article_partial_test.rb

require "view_partial_test_case"

class ArticlePartialTest < ViewPartialTestCase
  test "renders a link to itself" do
    article = Article.create! title: "Hello, world"

    render "articles/article", article: article

    assert_link article.title, href: article_url(article)
  end
end
```

More information about the assertions included by Capybara can be found in the
[Capybara Assertions](#capybara-assertions) section.

### Parsing View Content

Starting in Action View version 7.1, the `rendered` helper method returns an
object capable of parsing the view partial's rendered content.

To transform the `String` content returned by the `rendered` method into an
object, define a parser by calling
[`register_parser`](https://api.rubyonrails.org/classes/ActionView/TestCase/Behavior/ClassMethods.html#method-i-register_parser).
Calling `register_parser :rss` defines a `rendered.rss` helper method. For
example, to parse rendered [RSS content][] into an object with `rendered.rss`,
register a call to `RSS::Parser.parse`:

```ruby
register_parser :rss, -> rendered { RSS::Parser.parse(rendered) }

test "renders RSS" do
  article = Article.create!(title: "Hello, world")

  render formats: :rss, partial: article

  assert_equal "Hello, world", rendered.rss.items.last.title
end
```

By default, `ActionView::TestCase` defines a parser for:

* `:html` - returns an instance of
  [Nokogiri::XML::Node](https://nokogiri.org/rdoc/Nokogiri/XML/Node.html)
* `:json` - returns an instance of
  [ActiveSupport::HashWithIndifferentAccess](https://api.rubyonrails.org/classes/ActiveSupport/HashWithIndifferentAccess.html)

```ruby
test "renders HTML" do
  article = Article.create!(title: "Hello, world")

  render partial: "articles/article", locals: { article: article }

  assert_pattern { rendered.html.at("main h1") => { content: "Hello, world" } }
end

test "renders JSON" do
  article = Article.create!(title: "Hello, world")

  render formats: :json, partial: "articles/article", locals: { article: article }

  assert_pattern { rendered.json => { title: "Hello, world" } }
end
```

[rails-dom-testing]: https://github.com/rails/rails-dom-testing
[RSS content]: https://www.rssboard.org/rss-specification

### Additional View-Based Assertions

There are more assertions that are primarily used in testing views:

| Assertion                                                 | Purpose |
| --------------------------------------------------------- | ------- |
| `assert_dom_email`                                     | Allows you to make assertions on the body of an e-mail. |
| `assert_dom_encoded`                                   | Allows you to make assertions on encoded HTML. It does this by un-encoding the contents of each element and then calling the block with all the un-encoded elements.|
| `css_select(selector)` or `css_select(element, selector)` | Returns an array of all the elements selected by the _selector_. In the second variant it first matches the base _element_ and tries to match the _selector_ expression on any of its children. If there are no matches both variants return an empty array.|

Here's an example of using `assert_dom_email`:

```ruby
assert_dom_email do
  assert_dom "small", "Please click the 'Unsubscribe' link if you want to opt-out."
end
```

### Testing View Partials

[Partial](layouts_and_rendering.html#using-partials) templates - usually called
"partials" - can break the rendering process into more manageable chunks. With
partials, you can extract sections of code from your views to separate files and
reuse them in multiple places.

View tests provide an opportunity to test that partials render content the way
you expect. View partial tests can be stored in `test/views/` and inherit from
`ActionView::TestCase`.

To render a partial, call `render` like you would in a template. The content is
available through the test-local `rendered` method:

```ruby
class ArticlePartialTest < ActionView::TestCase
  test "renders a link to itself" do
    article = Article.create! title: "Hello, world"

    render "articles/article", article: article

    assert_includes rendered, article.title
  end
end
```

Tests that inherit from `ActionView::TestCase` also have access to
[`assert_dom`](#testing-views) and the [other additional view-based
assertions](#additional-view-based-assertions) provided by
[rails-dom-testing][]:

```ruby
test "renders a link to itself" do
  article = Article.create! title: "Hello, world"

  render "articles/article", article: article

  assert_dom "a[href=?]", article_url(article), text: article.title
end
```

### Testing View Helpers

A helper is a module where you can define methods which are available in your
views.

In order to test helpers, all you need to do is check that the output of the
helper method matches what you'd expect. Tests related to the helpers are
located under the `test/helpers` directory.

Given we have the following helper:

```ruby
module UsersHelper
  def link_to_user(user)
    link_to "#{user.first_name} #{user.last_name}", user
  end
end
```

We can test the output of this method like this:

```ruby
class UsersHelperTest < ActionView::TestCase
  test "should return the user's full name" do
    user = users(:david)

    assert_dom_equal %{<a href="/user/#{user.id}">David Heinemeier Hansson</a>}, link_to_user(user)
  end
end
```

Moreover, since the test class extends from `ActionView::TestCase`, you have
access to Rails' helper methods such as `link_to` or `pluralize`.

Testing Mailers
---------------

Your mailer classes - like every other part of your Rails application - should
be tested to ensure that they are working as expected.

The goals of testing your mailer classes are to ensure that:

* emails are being processed (created and sent)
* the email content is correct (subject, sender, body, etc)
* the right emails are being sent at the right times

There are two aspects of testing your mailer, the unit tests and the functional
tests. In the unit tests, you run the mailer in isolation with tightly
controlled inputs and compare the output to a known value (a
[fixture](#fixtures)). In the functional tests you don't so much test the
details produced by the mailer; instead, you test that the controllers and
models are using the mailer in the right way. You test to prove that the right
email was sent at the right time.

### Unit Testing

In order to test that your mailer is working as expected, you can use unit tests
to compare the actual results of the mailer with pre-written examples of what
should be produced.

#### Mailer Fixtures

For the purposes of unit testing a mailer, fixtures are used to provide an
example of how the output _should_ look. Because these are example emails, and
not Active Record data like the other fixtures, they are kept in their own
subdirectory apart from the other fixtures. The name of the directory within
`test/fixtures` directly corresponds to the name of the mailer. So, for a mailer
named `UserMailer`, the fixtures should reside in `test/fixtures/user_mailer`
directory.

If you generated your mailer, the generator does not create stub fixtures for
the mailers actions. You'll have to create those files yourself as described
above.

#### The Basic Test Case

Here's a unit test to test a mailer named `UserMailer` whose action `invite` is
used to send an invitation to a friend:

```ruby
require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.create_invite("me@example.com",
                                     "friend@example.com", Time.now)

    # Send the email, then test that it got queued
    assert_emails 1 do
      email.deliver_now
    end

    # Test the body of the sent email contains what we expect it to
    assert_equal ["me@example.com"], email.from
    assert_equal ["friend@example.com"], email.to
    assert_equal "You have been invited by me@example.com", email.subject
    assert_equal read_fixture("invite").join, email.body.to_s
  end
end
```

In the test the email is created and the returned object is stored in the
`email` variable. The first assert checks it was sent, then, in the second batch
of assertions, the email contents are checked. The helper `read_fixture` is used
to read in the content from this file.

NOTE: `email.body.to_s` is present when there's only one (HTML or text) part
present. If the mailer provides both, you can test your fixture against specific
parts with `email.text_part.body.to_s` or `email.html_part.body.to_s`.

Here's the content of the `invite` fixture:

```
Hi friend@example.com,

You have been invited.

Cheers!
```

#### Configuring the Delivery Method for Test

The line `ActionMailer::Base.delivery_method = :test` in
`config/environments/test.rb` sets the delivery method to test mode so that the
email will not actually be delivered (useful to avoid spamming your users while
testing). Instead, the email will be appended to an array
(`ActionMailer::Base.deliveries`).

NOTE: The `ActionMailer::Base.deliveries` array is only reset automatically in
`ActionMailer::TestCase` and `ActionDispatch::IntegrationTest` tests. If you
want to have a clean slate outside these test cases, you can reset it manually
with: `ActionMailer::Base.deliveries.clear`

#### Testing Enqueued Emails

You can use the `assert_enqueued_email_with` assertion to confirm that the email
has been enqueued with all of the expected mailer method arguments and/or
parameterized mailer parameters. This allows you to match any emails that have
been enqueued with the `deliver_later` method.

As with the basic test case, we create the email and store the returned object
in the `email` variable. The following examples include variations of passing
arguments and/or parameters.

This example will assert that the email has been enqueued with the correct
arguments:

```ruby
require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.create_invite("me@example.com", "friend@example.com")

    # Test that the email got enqueued with the correct arguments
    assert_enqueued_email_with UserMailer, :create_invite, args: ["me@example.com", "friend@example.com"] do
      email.deliver_later
    end
  end
end
```

This example will assert that a mailer has been enqueued with the correct mailer
method named arguments by passing a hash of the arguments as `args`:

```ruby
require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.create_invite(from: "me@example.com", to: "friend@example.com")

    # Test that the email got enqueued with the correct named arguments
    assert_enqueued_email_with UserMailer, :create_invite,
    args: [{ from: "me@example.com", to: "friend@example.com" }] do
      email.deliver_later
    end
  end
end
```

This example will assert that a parameterized mailer has been enqueued with the
correct parameters and arguments. The mailer parameters are passed as `params`
and the mailer method arguments as `args`:

```ruby
require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.with(all: "good").create_invite("me@example.com", "friend@example.com")

    # Test that the email got enqueued with the correct mailer parameters and arguments
    assert_enqueued_email_with UserMailer, :create_invite,
    params: { all: "good" }, args: ["me@example.com", "friend@example.com"] do
      email.deliver_later
    end
  end
end
```

This example shows an alternative way to test that a parameterized mailer has
been enqueued with the correct parameters:

```ruby
require "test_helper"

class UserMailerTest < ActionMailer::TestCase
  test "invite" do
    # Create the email and store it for further assertions
    email = UserMailer.with(to: "friend@example.com").create_invite

    # Test that the email got enqueued with the correct mailer parameters
    assert_enqueued_email_with UserMailer.with(to: "friend@example.com"), :create_invite do
      email.deliver_later
    end
  end
end
```

### Functional and System Testing

Unit testing allows us to test the attributes of the email while functional and
system testing allows us to test whether user interactions appropriately trigger
the email to be delivered. For example, you can check that the invite friend
operation is sending an email appropriately:

```ruby
# Integration Test
require "test_helper"

class UsersControllerTest < ActionDispatch::IntegrationTest
  test "invite friend" do
    # Asserts the difference in the ActionMailer::Base.deliveries
    assert_emails 1 do
      post invite_friend_url, params: { email: "friend@example.com" }
    end
  end
end
```

```ruby
# System Test
require "test_helper"

class UsersTest < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :headless_chrome

  test "inviting a friend" do
    visit invite_users_url
    fill_in "Email", with: "friend@example.com"
    assert_emails 1 do
      click_on "Invite"
    end
  end
end
```

NOTE: The `assert_emails` method is not tied to a particular deliver method and
will work with emails delivered with either the `deliver_now` or `deliver_later`
method. If we explicitly want to assert that the email has been enqueued we can
use the `assert_enqueued_email_with` ([examples
above](#testing-enqueued-emails)) or `assert_enqueued_emails` methods. More
information can be found in the
[documentation](https://api.rubyonrails.org/classes/ActionMailer/TestHelper.html).

Testing Jobs
------------

Jobs can be tested in isolation (focusing on the job's behavior) and in context
(focusing on the calling code's behavior).

### Testing Jobs in Isolation

When you generate a job, an associated test file will also be generated in the
`test/jobs` directory.

Here is a test you could write for a billing job:

```ruby
require "test_helper"

class BillingJobTest < ActiveJob::TestCase
  test "account is charged" do
    perform_enqueued_jobs do
      BillingJob.perform_later(account, product)
    end
    assert account.reload.charged_for?(product)
  end
end
```

The default queue adapter for tests will not perform jobs until
[`perform_enqueued_jobs`][] is called. Additionally, it will clear all jobs
before each test is run so that tests do not interfere with each other.

The test uses `perform_enqueued_jobs` and [`perform_later`][] instead of
[`perform_now`][] so that if retries are configured, retry failures are caught
by the test instead of being re-enqueued and ignored.

[`perform_enqueued_jobs`]:
    https://api.rubyonrails.org/classes/ActiveJob/TestHelper.html#method-i-perform_enqueued_jobs
[`perform_later`]:
    https://api.rubyonrails.org/classes/ActiveJob/Enqueuing/ClassMethods.html#method-i-perform_later
[`perform_now`]:
    https://api.rubyonrails.org/classes/ActiveJob/Execution/ClassMethods.html#method-i-perform_now

### Testing Jobs in Context

It's good practice to test that jobs are correctly enqueued, for example, by a
controller action. The [`ActiveJob::TestHelper`][] module provides several
methods that can help with this, such as [`assert_enqueued_with`][].

Here is an example that tests an account model method:

```ruby
require "test_helper"

class AccountTest < ActiveSupport::TestCase
  include ActiveJob::TestHelper

  test "#charge_for enqueues billing job" do
    assert_enqueued_with(job: BillingJob) do
      account.charge_for(product)
    end

    assert_not account.reload.charged_for?(product)

    perform_enqueued_jobs

    assert account.reload.charged_for?(product)
  end
end
```

[`ActiveJob::TestHelper`]:
    https://api.rubyonrails.org/classes/ActiveJob/TestHelper.html
[`assert_enqueued_with`]:
    https://api.rubyonrails.org/classes/ActiveJob/TestHelper.html#method-i-assert_enqueued_with

### Testing that Exceptions are Raised

Testing that your job raises an exception in certain cases can be tricky,
especially when you have retries configured. The `perform_enqueued_jobs` helper
fails any test where a job raises an exception, so to have the test succeed when
the exception is raised you have to call the job's `perform` method directly.

```ruby
require "test_helper"

class BillingJobTest < ActiveJob::TestCase
  test "does not charge accounts with insufficient funds" do
    assert_raises(InsufficientFundsError) do
      BillingJob.new(empty_account, product).perform
    end
    assert_not account.reload.charged_for?(product)
  end
end
```

This method is not recommended in general, as it circumvents some parts of the
framework, such as argument serialization.

Testing Action Cable
--------------------

Since Action Cable is used at different levels inside your application, you'll
need to test both the channels, connection classes themselves, and that other
entities broadcast correct messages.

### Connection Test Case

By default, when you generate a new Rails application with Action Cable, a test
for the base connection class (`ApplicationCable::Connection`) is generated as
well under `test/channels/application_cable` directory.

Connection tests aim to check whether a connection's identifiers get assigned
properly or that any improper connection requests are rejected. Here is an
example:

```ruby
class ApplicationCable::ConnectionTest < ActionCable::Connection::TestCase
  test "connects with params" do
    # Simulate a connection opening by calling the `connect` method
    connect params: { user_id: 42 }

    # You can access the Connection object via `connection` in tests
    assert_equal connection.user_id, "42"
  end

  test "rejects connection without params" do
    # Use `assert_reject_connection` matcher to verify that
    # connection is rejected
    assert_reject_connection { connect }
  end
end
```

You can also specify request cookies the same way you do in integration tests:

```ruby
test "connects with cookies" do
  cookies.signed[:user_id] = "42"

  connect

  assert_equal connection.user_id, "42"
end
```

See the API documentation for
[`ActionCable::Connection::TestCase`](https://api.rubyonrails.org/classes/ActionCable/Connection/TestCase.html)
for more information.

### Channel Test Case

By default, when you generate a channel, an associated test will be generated as
well under the `test/channels` directory. Here's an example test with a chat
channel:

```ruby
require "test_helper"

class ChatChannelTest < ActionCable::Channel::TestCase
  test "subscribes and stream for room" do
    # Simulate a subscription creation by calling `subscribe`
    subscribe room: "15"

    # You can access the Channel object via `subscription` in tests
    assert subscription.confirmed?
    assert_has_stream "chat_15"
  end
end
```

This test is pretty simple and only asserts that the channel subscribes the
connection to a particular stream.

You can also specify the underlying connection identifiers. Here's an example
test with a web notifications channel:

```ruby
require "test_helper"

class WebNotificationsChannelTest < ActionCable::Channel::TestCase
  test "subscribes and stream for user" do
    stub_connection current_user: users(:john)

    subscribe

    assert_has_stream_for users(:john)
  end
end
```

See the API documentation for
[`ActionCable::Channel::TestCase`](https://api.rubyonrails.org/classes/ActionCable/Channel/TestCase.html)
for more information.

### Custom Assertions And Testing Broadcasts Inside Other Components

Action Cable ships with a bunch of custom assertions that can be used to lessen
the verbosity of tests. For a full list of available assertions, see the API
documentation for
[`ActionCable::TestHelper`](https://api.rubyonrails.org/classes/ActionCable/TestHelper.html).

It's a good practice to ensure that the correct message has been broadcasted
inside other components (e.g. inside your controllers). This is precisely where
the custom assertions provided by Action Cable are pretty useful. For instance,
within a model:

```ruby
require "test_helper"

class ProductTest < ActionCable::TestCase
  test "broadcast status after charge" do
    assert_broadcast_on("products:#{product.id}", type: "charged") do
      product.charge(account)
    end
  end
end
```

If you want to test the broadcasting made with `Channel.broadcast_to`, you
should use `Channel.broadcasting_for` to generate an underlying stream name:

```ruby
# app/jobs/chat_relay_job.rb
class ChatRelayJob < ApplicationJob
  def perform(room, message)
    ChatChannel.broadcast_to room, text: message
  end
end
```

```ruby
# test/jobs/chat_relay_job_test.rb
require "test_helper"

class ChatRelayJobTest < ActiveJob::TestCase
  include ActionCable::TestHelper

  test "broadcast message to room" do
    room = rooms(:all)

    assert_broadcast_on(ChatChannel.broadcasting_for(room), text: "Hi!") do
      ChatRelayJob.perform_now(room, "Hi!")
    end
  end
end
```

Running tests in Continuous Integration (CI)
--------------------------------------------

Continuous Integration (CI) is a development practice where changes are
frequently integrated into the main codebase, and as such, are automatically
tested before merge.

To run all tests in a CI environment, there's just one command you need:

```bash
$ bin/rails test
```

If you are using [System Tests](#system-testing), `bin/rails test` will not run
them, since they can be slow. To also run them, add another CI step that runs
`bin/rails test:system`, or change your first step to `bin/rails test:all`,
which runs all tests including system tests.

Parallel Testing
----------------

Running tests in parallel reduces the time it takes your entire test suite to
run. While forking processes is the default method, threading is supported as
well.

### Parallel Testing with Processes

The default parallelization method is to fork processes using Ruby's DRb system.
The processes are forked based on the number of workers provided. The default
number is the actual core count on the machine, but can be changed by the number
passed to the `parallelize` method.

To enable parallelization add the following to your `test_helper.rb`:

```ruby
class ActiveSupport::TestCase
  parallelize(workers: 2)
end
```

The number of workers passed is the number of times the process will be forked.
You may want to parallelize your local test suite differently from your CI, so
an environment variable is provided to be able to easily change the number of
workers a test run should use:

```bash
$ PARALLEL_WORKERS=15 bin/rails test
```

When parallelizing tests, Active Record automatically handles creating a
database and loading the schema into the database for each process. The
databases will be suffixed with the number corresponding to the worker. For
example, if you have 2 workers the tests will create `test-database-0` and
`test-database-1` respectively.

If the number of workers passed is 1 or fewer the processes will not be forked
and the tests will not be parallelized and they will use the original
`test-database` database.

Two hooks are provided, one runs when the process is forked, and one runs before
the forked process is closed. These can be useful if your app uses multiple
databases or performs other tasks that depend on the number of workers.

The `parallelize_setup` method is called right after the processes are forked.
The `parallelize_teardown` method is called right before the processes are
closed.

```ruby
class ActiveSupport::TestCase
  parallelize_setup do |worker|
    # setup databases
  end

  parallelize_teardown do |worker|
    # cleanup databases
  end

  parallelize(workers: :number_of_processors)
end
```

These methods are not needed or available when using parallel testing with
threads.

### Parallel Testing with Threads

If you prefer using threads or are using JRuby, a threaded parallelization
option is provided. The threaded parallelizer is backed by minitest's
`Parallel::Executor`.

To change the parallelization method to use threads over forks put the following
in your `test_helper.rb`:

```ruby
class ActiveSupport::TestCase
  parallelize(workers: :number_of_processors, with: :threads)
end
```

Rails applications generated from JRuby or TruffleRuby will automatically
include the `with: :threads` option.

NOTE: As in the section above, you can also use the environment variable
`PARALLEL_WORKERS` in this context, to change the number of workers your test
run should use.

### Testing Parallel Transactions

When you want to test code that runs parallel database transactions in threads,
those can block each other because they are already nested under the implicit
test transaction.

To workaround this, you can disable transactions in a test case class by setting
`self.use_transactional_tests = false`:

```ruby
class WorkerTest < ActiveSupport::TestCase
  self.use_transactional_tests = false

  test "parallel transactions" do
    # start some threads that create transactions
  end
end
```

NOTE: With disabled transactional tests, you have to clean up any data tests
create as changes are not automatically rolled back after the test completes.

### Threshold to Parallelize tests

Running tests in parallel adds an overhead in terms of database setup and
fixture loading. Because of this, Rails won't parallelize executions that
involve fewer than 50 tests.

You can configure this threshold in your `test.rb`:

```ruby
config.active_support.test_parallelization_threshold = 100
```

And also when setting up parallelization at the test case level:

```ruby
class ActiveSupport::TestCase
  parallelize threshold: 100
end
```

Testing Eager Loading
---------------------

Normally, applications do not eager load in the `development` or `test`
environments to speed things up. But they do in the `production` environment.

If some file in the project cannot be loaded for whatever reason, it is
important to detect it before deploying to production.

### Continuous Integration

If your project has CI in place, eager loading in CI is an easy way to ensure
the application eager loads.

CIs typically set an environment variable to indicate the test suite is running
there. For example, it could be `CI`:

```ruby
# config/environments/test.rb
config.eager_load = ENV["CI"].present?
```

Starting with Rails 7, newly generated applications are configured that way by
default.

If your project does not have continuous integration, you can still eager load
in the test suite by calling `Rails.application.eager_load!`:

```ruby
require "test_helper"

class ZeitwerkComplianceTest < ActiveSupport::TestCase
  test "eager loads all files without errors" do
    assert_nothing_raised { Rails.application.eager_load! }
  end
end
```

Additional Testing Resources
----------------------------

### Errors

In system tests, integration tests and functional controller tests, Rails will
attempt to rescue from errors raised and respond with HTML error pages by
default. This behavior can be controlled by the
[`config.action_dispatch.show_exceptions`](/configuring.html#config-action-dispatch-show-exceptions)
configuration.

### Testing Time-Dependent Code

Rails provides built-in helper methods that enable you to assert that your
time-sensitive code works as expected.

The following example uses the [`travel_to`][travel_to] helper:

```ruby
# Given a user is eligible for gifting a month after they register.
user = User.create(name: "Gaurish", activation_date: Date.new(2004, 10, 24))
assert_not user.applicable_for_gifting?

travel_to Date.new(2004, 11, 24) do
  # Inside the `travel_to` block `Date.current` is stubbed
  assert_equal Date.new(2004, 10, 24), user.activation_date
  assert user.applicable_for_gifting?
end

# The change was visible only inside the `travel_to` block.
assert_equal Date.new(2004, 10, 24), user.activation_date
```

Please see [`ActiveSupport::Testing::TimeHelpers`][time_helpers_api] API
reference for more information about the available time helpers.

[travel_to]:
    https://api.rubyonrails.org/classes/ActiveSupport/Testing/TimeHelpers.html#method-i-travel_to
[time_helpers_api]:
    https://api.rubyonrails.org/classes/ActiveSupport/Testing/TimeHelpers.html
