We are sorry for the troubles and thanks for reporting! Please simply delete (or don't copy) the SpineTests directory.
This documentation section seems to be missing an update where it should now say "Copy the Spine and Spine Examples directories". When copying SpineTests it is also necessary to copy spine-csharp/tests, however you will not want to use the tests anyway. To prevent future troubles, we will move SpineTests from Assets to Modules so that accidental copying can no longer happen.
We just pushed a commit to the 4.0 branch that moves the tests directory from the spine-unity/Assets directory to its own UPM module directory. This should hopefully prevent future troubles.
