Before:
  call ale#assert#SetUpLinterTest('elixir', 'mix')
  call ale#test#SetFilename('elixir_paths/mix_project/lib/app.ex')
  let g:env_prefix = ale#Env('MIX_BUILD_PATH', 'TEMP_DIR')

After:
  unlet! g:env_prefix

  call ale#assert#TearDownLinterTest()

Execute(The default mix command should be correct):
  AssertLinterCwd ale#path#Simplify(g:dir . '/elixir_paths/mix_project')
  AssertLinter 'mix', g:env_prefix . 'mix compile %s'

Execute(Build mix commands with an umbrella root):
  call ale#test#SetFilename('elixir_paths/umbrella_project/apps/mix_project/lib/app.ex')

  AssertLinterCwd ale#path#Simplify(g:dir . '/elixir_paths/umbrella_project')
  AssertLinter 'mix', g:env_prefix . 'mix compile %s'