Tests: add option to build one binary per GTest file

Bundling many tests in a single binary reduces build time and disk space
usage, but is less convenient for running individual tests command line
as filter flags need to be used.

This adds WITH_TESTS_SINGLE_BINARY to generate one executable file per
source file. Note that enabling this option requires a significant amount
of disk space.

Due to refactoring, the resulting ctest names are a bit different than
before. The number of tests is also a bit different depending if this
option is used, as one uses gtests discovery and the other is organized
purely by filename, which isn't always 1:1.

Co-authored-by: Sergey Sharybin <sergey@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/114604

tests/gtests/CMakeLists.txt

@@ -7,7 +7,9 @@ if(WITH_GTESTS)
   remove_strict_flags()
 
   # Build common test executable used by most tests
-  add_subdirectory(runner)
+  if(WITH_TESTS_SINGLE_BINARY)
+    add_subdirectory(runner)
+  endif()
 
   # Build utility library used by test executables
   add_subdirectory(testing)

tests/gtests/runner/CMakeLists.txt

@@ -32,7 +32,6 @@ blender_src_gtest_ex(
   NAME blender
   SRC "${SRC}"
   EXTRA_LIBS "${TEST_LIBS}"
-  SKIP_ADD_TEST
 )
 setup_platform_linker_libs(blender_test)