Enhanced the test cases for xcf files

PR Goal

The test case judges whether the generated image is expected by directly comparing the difference between the two image files

Use this ImageHash library to do this

[x] If relevant, manual tests have been done to ensure the stability of the whole application and that the involved feature works
[ ] Automated tests covering the feature or the fix, have been written, deemed irrelevant (give the reason), or an issue has been created to implement the test (give the link) This is a test case in itself, so there is no test case for it.
[x] The PR or the original issue contains a short summary of the implemented solution.