Before:
  runtime ale_linters/elixir/mix.vim

  call ale#test#SetDirectory('/testplugin/test/command_callback')

  let g:env_prefix = has('win32')
  \ ? 'set MIX_BUILD_PATH=TEMP && '
  \ : 'MIX_BUILD_PATH=TEMP '


  function! GetCommand() abort
    let l:command = ale_linters#elixir#mix#GetCommand(bufnr(''))

    let l:split_command = split(l:command, 'MIX_BUILD_PATH=[^ ]*\s')

    return l:split_command[0] . 'MIX_BUILD_PATH=TEMP' .  l:split_command[1]
  endfunction



After:
  Restore

  unlet! g:env_prefix

  call ale#linter#Reset()
  call ale#test#RestoreDirectory()

  delfunction GetCommand

Execute(The default mix command should be correct):
  AssertEqual
  \ GetCommand(),
  \ 'cd '''' && '
  \ . g:env_prefix
  \ . 'mix compile %s'