From: Gentoo Authors
Subject: [PATCH] Write test output to the build directory

Keep the source tree read-only, as required by cmake.eclass.

--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -4,7 +4,7 @@
     return()
 endif()
 
-set(PDF_TEST_OUTPUT_PATH "${CMAKE_CURRENT_SOURCE_DIR}/out")
+set(PDF_TEST_OUTPUT_PATH "${CMAKE_CURRENT_BINARY_DIR}/out")
 make_directory(${PDF_TEST_OUTPUT_PATH})
 
 file(TO_NATIVE_PATH "${PDF_TEST_RESOURCE_PATH}" PDF_TEST_RESOURCE_PATH)