Write a test that invokes the __str__ method of the StratisCliActionError, which is the head of the exception chain

[mulkieran]

Our tests seem to be built to never do that, since this error just contains context about how the method was called. This one is potentially a bit tricky, and might involve manipulating the behavior of the interpreter. But it might turn out to involve something pretty straightforward as well.

[mulkieran]

Actually, I would call this one the easiest of all. Extend RunTestCase::error_check to ensure that the string is non-empty and is a str, and this one would be done.