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

After:
  call ale#test#RestoreDirectory()

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

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

Execute(ale#python#PipenvPresent is false when no pipenv environment is present):
  call ale#test#SetFilename('test-files/python/no_pipenv/whatever.py')

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