tests: Smoke test `__str__()` and `__repr__()`
tests: Smoke test `__str__()` and `__repr__()`

It is extremely annoying to have an error obscured by an exception in
repr or str.  The concrete output of str and repr, however, is bound to
change and therefore, it needs not be tested.

Synss/python-mbedtls,Synss/python-mbedtls