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

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

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

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