Unitettesting: Force python errors to show as error

tests/python/render_layer/CMakeLists.txt

@@ -54,6 +54,7 @@ macro(RENDER_LAYER_TEST test_name)
 	# things from render_layer_common.py
 	add_test(render_layer_${test_name} ${TEST_BLENDER_EXE}
 		--python-expr "import sys; sys.path.append('${CMAKE_CURRENT_LIST_DIR}')"
+		--python-exit-code 1
 		--python ${CMAKE_CURRENT_LIST_DIR}/test_${test_name}.py --
 		--testdir="${TEST_SRC_DIR}/layers"
 	)