Why does this package not correspond to the file-path (IntelliJ test-folder)?

in order to use the built-in IntelliJ test-coverage tool, I had to mark the package containing the tests as a "test"-folder (In Project Structure).

Unfortunately, when I did this I suddenly got the error "Package name '..' does not correspond to the file path". Before the folder was marked as a test folder, this was not an issue.

Below is a screenshot showing the project structure and the error:

Any help on how to resolve this would be truly appreciated!