Pull request failed one check due to absence of test file

I resolved the issue. I have checked it in my pc. But I don't know what a test file is. So I am not able to successfully create my pull request. It would be very helpful someone can tell me what I have to show in test file? I have also attached the picture of the dialogue after resolving the issue (in the above link).

This means that there must be automated tests. Which are handled here at Joplin with the test framework Jest.