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

After:
  call ale#test#RestoreDirectory()

Execute(Detect root of Python project with .flake8 correctly):
  call ale#test#SetFilename('python-test-files/python-package-project/package-name/module.py')
  AssertEqual
  \ ale#path#Simplify(g:dir . '/python-test-files/python-package-project'),
  \ ale#python#FindProjectRoot(bufnr(''))