Use the right diff tool.

scripts/cmake/test/AddTest.cmake

@@ -101,8 +101,10 @@ function (AddTest)
 	endif()
 
 	if(AddTest_TESTER STREQUAL "diff")
+		set(SELECTED_DIFF_TOOL_PATH ${DIFF_TOOL_PATH})
 		set(TESTER_ARGS "-sbB")
 	elseif(AddTest_TESTER STREQUAL "numdiff")
+		set(SELECTED_DIFF_TOOL_PATH ${NUMDIFF_TOOL_PATH})
 		set(TESTER_ARGS "--statistics --absolute-tolerance=1e-5 --relative-tolerance=1e-4")
 	endif()
 
@@ -111,7 +113,7 @@ function (AddTest)
 			get_filename_component(FILE_NAME ${FILE} NAME_WE)
 			get_filename_component(FILE_EXT ${FILE} EXT)
 			set(FILE_EXPECTED ${FILE_NAME}_expected${FILE_EXT})
-			set(TESTER_COMMAND ${TESTER_COMMAND} "${NUMDIFF_TOOL_PATH} ${TESTER_ARGS} DATA{${AddTest_SOURCE_PATH}/${FILE_EXPECTED}} ${AddTest_BINARY_PATH}/${FILE}")
+			set(TESTER_COMMAND ${TESTER_COMMAND} "${SELECTED_DIFF_TOOL_PATH} ${TESTER_ARGS} DATA{${AddTest_SOURCE_PATH}/${FILE_EXPECTED}} ${AddTest_BINARY_PATH}/${FILE}")
 			if(AddTest_DIFF_DATA_PARSED)
 				set(AddTest_DIFF_DATA_PARSED "${AddTest_DIFF_DATA_PARSED},${FILE_EXPECTED}")
 			else()