Move test suite to Pytest (replace Behave)

[wren]

Fixes #1192

Moves test suite entirely into pytest from behave.

[micahellison]

I'm getting some IO and recursion errors while running these on Windows. These repeats a ton:

 Traceback (most recent call last):
    File "c:\users\micah\.pyenv\pyenv-win\versions\3.8.2\lib\tempfile.py", line 803, in onerror
      _os.unlink(path)
  PermissionError: [WinError 5] Access is denied: 'C:\\Users\\micah\\AppData\\Local\\Temp\\tmpyzro5wbt'

  During handling of the above exception, another exception occurred:

  Traceback (most recent call last):
    File "c:\users\micah\.pyenv\pyenv-win\versions\3.8.2\lib\shutil.py", line 617, in _rmtree_unsafe
      os.rmdir(path)
  PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: 'C:\\Users\\micah\\AppData\\Local\\Temp\\tmpyzro5wbt'

  During handling of the above exception, another exception occurred:

  Traceback (most recent call last):
    File "c:\users\micah\.pyenv\pyenv-win\versions\3.8.2\lib\tempfile.py", line 803, in onerror
      _os.unlink(path)
  PermissionError: [WinError 5] Access is denied: 'C:\\Users\\micah\\AppData\\Local\\Temp\\tmpyzro5wbt'

  During handling of the above exception, another exception occurred:

  Traceback (most recent call last):
    File "c:\users\micah\.pyenv\pyenv-win\versions\3.8.2\lib\shutil.py", line 617, in _rmtree_unsafe
      os.rmdir(path)
  PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: 'C:\\Users\\micah\\AppData\\Local\\Temp\\tmpyzro5wbt'

  During handling of the above exception, another exception occurred:

And at the end, I get:

 RecursionError: maximum recursion depth exceeded while calling a Python object

    warnings.warn(pytest.PytestUnraisableExceptionWarning(msg))

-- Docs: https://docs.pytest.org/en/stable/warnings.html

[MinchinWeb]

As a headsup, I discovered today that the current behave test suite does not run as expected (at all?) if not run from the project root folder.

[micahellison]

Let's move off of pyflakes, probably to pylint, maaaaybe to flake8, though pylint looks better at first glance.

[micahellison]

🧪