Before:
  function! MockAlwaysGetCompletions() abort
    let g:get_completions_called = 0

    function! ale#completion#AlwaysGetCompletions() abort
      let g:get_completions_called = 1
    endfunction
  endfunction

  call MockAlwaysGetCompletions()

After:
  unlet! g:get_completions_called
  delfunction MockAlwaysGetCompletions
  delfunction ale#completion#AlwaysGetCompletions

  runtime autoload/ale/completion.vim

Execute(ale#completion#AlwaysGetCompletions should be called when ALEComplete is executed):
  AssertEqual 0, g:get_completions_called
  ALEComplete
  AssertEqual 1, g:get_completions_called