Tests: Run without creating thumbnails by default

This reduces the thumbnails generated by a tests run from about
5k to less than 10.

In practice, some tests can still reset this userpreference e.g. by calling
`bpy.ops.wm.read_factory_settings()`. Further tweaks are possible
should this still be an issue in the future.

See also blender/blender#153811 and infrastructure/meta#197

Co-authored-by: Bastien Montagne <bastien@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/153817

tests/CMakeLists.txt

@@ -54,7 +54,20 @@ endif()
 # Standard Blender arguments for running tests.
 # Specify exit code so that if a Python script error happens, the test fails.
 set(TEST_BLENDER_EXE_PARAMS
-  --background --factory-startup --debug-memory --debug-exit-on-error --python-exit-code 1
+  --background
+  --factory-startup
+  --debug-memory
+  --debug-exit-on-error
+  --python-exit-code 1
+)
+
+# The `TEST_BLENDER_EXE_PARAMS` list might be edited in some cases (see e.g. `add_blender_test_allow_error`).
+# This will break in case a parameter contains a `;` that should remain literal,
+# instead of being interpreted as a list item separator by CMake.
+# So this additional variable is always added after `TEST_BLENDER_EXE_PARAMS`, always as-is.
+set(TEST_BLENDER_EXE_PARAMS_NO_THUMB
+  # Python expression to disable thumbnails creation on blendfile saving.
+  --python-expr [=[import bpy\;bpy.context.preferences.filepaths.file_preview_type='NONE']=]
 )
 
 # Python CTests

tests/python/CMakeLists.txt

@@ -52,6 +52,7 @@ function(add_blender_test testname)
     ""
     "${TEST_BLENDER_EXE}"
     ${TEST_BLENDER_EXE_PARAMS}
+    "${TEST_BLENDER_EXE_PARAMS_NO_THUMB}"
     ${ARGN}
   )
 endfunction()
@@ -66,6 +67,7 @@ function(add_blender_test_allow_error testname)
     ""
     "${TEST_BLENDER_EXE}"
     ${EXE_PARAMS}
+    "${TEST_BLENDER_EXE_PARAMS_NO_THUMB}"
     ${ARGN}
   )
 endfunction()
@@ -125,6 +127,7 @@ if(WITH_UI_TESTS)
       -p 0 0 800 600
       --gpu-backend ${backend}
       "${EXE_PARAMS}"
+      "${TEST_BLENDER_EXE_PARAMS_NO_THUMB}"
       "${ARGN}"
     )
   endfunction()