test CI
Debugging an issue noted in https://github.com/pandas-dev/pandas/pull/30139 and maybe in https://github.com/pandas-dev/pandas/pull/30245
Hopefully fixed by https://github.com/pandas-dev/pandas/pull/30293/commits/c31ee5adaf4034b0549e2e26e93f0702ded75678. Will leave the lint failure in just to check. Good. Failed with

```
3.7.9 (flake8-comprehensions: 3.1.4, mccabe: 0.6.1, pycodestyle: 2.5.0, pyflakes: 2.1.1) CPython 3.7.3 on Linux
Linting .py code
##[error]./pandas/core/arrays/sparse/array.py:4:1:F401:'unittest' imported but unused
Linting .py code DONE
```