Before:
  function! MockAlwaysGetCompletions() abort
    let g:get_completions_called = 0
    let g:always_get_completions_argument = -1

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

  call MockAlwaysGetCompletions()

After:
  unlet! g:get_completions_called
  unlet! g:always_get_completions_argument
  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
  AssertEqual 0, g:always_get_completions_argument