I am trying to deploy a change set which includes to classes and a test class.
For validation I am only running two test classes, one which is included in the set and one which is already in production.

This scenario fails with Fatal Error and 0% coverage for all classes.
If I run the same validation with only one test class running then I don't get the fatal error but the coverage is not enough

Can someone help, why the first scenario with the two test classes is not working?