How do you test this?

Both `python tests/test_simple.py` and `python -m unittest discover` throw errors because of the import

```
  File "sampleproject/tests/test_simple.py", line 7, in <module>
    from sample.simple import add_one
ModuleNotFoundError: No module named 'sample'
```

So what's the correct way to test this package and other packages while in development?