I prefer tests to pass without warnings or in fact any extra output to stdout/stderr.  This should be easy to arrange by adding a
```
with warnings.catch_warnings():
   self.assertEqual(function_that_causes_the_warning(...), ...)
```
We could even test the spelling of the warning with
```
with warnings.catch_warnings(record=True) as w:
   self.assertEqual(function_that_causes_the_warning(...), ...)
   self.assertEqual(w, ['...'])
```
but I'm not convinced it's worth the effort.