Add test for non valid strings

[uriva]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 109

• 0 of 0 changed or added relevant lines in 0 files are covered.
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Change from base Build 107:	0.0%
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💛 - Coveralls

[jaraco]

This is interesting. In particular, it's interesting that the tests pass on Python 3.6 and 3.7, but not older versions. I'm curious to know why the error only happens on older Pythons.

I'm not sure this kind of test belongs in that file - I've always imagined that file to represent the canonical usage, not abbarant usage. I think I'd prefer for tests like these to be captured separately, probably through a separate unit test, maybe parameterized.