Before:
  call ale#test#SetDirectory('/testplugin/test')

After:
  call ale#test#RestoreDirectory()

Execute(ale#python#poetryPresent is true when a poetry environment is present):
  call ale#test#SetFilename('test-files/python/poetry/whatever.py')

  AssertEqual
  \  ale#python#PoetryPresent(bufnr('%')),
  \  1

Execute(ale#python#poetryPresent is false when no poetry environment is present):
  call ale#test#SetFilename('test-files/python/no_poetry/whatever.py')

  AssertEqual
  \  ale#python#PoetryPresent(bufnr('%')),
  \  0
