Since the side effect we're testing is part of the constructor call, and hence `client` is never actually assigned or deleted, I'd suggest we just eliminate the variable, viz:

```
    with pytest.raises(ValueError):
        KISSmetrics.Client(key='foo', trk_scheme='ssh')
```

This would also go for lines 61/62 below.  I wouldn't usually care enough to point this out but in the spirit of being Super Hygienic on this code base, I figured I'd suggest it.