Before:
  unlet! b:ale_completion_info
  unlet! b:ale_completion_result

  let b:lsp_started = 0

  runtime autoload/ale/lsp_linter.vim

  function! ale#lsp_linter#StartLSP(buffer, linter, Callback) abort
    return b:lsp_started
  endfunction

  function! SetCompletionResult(...) abort
    let b:ale_completion_result = ['foo']
  endfunction

  function! SetCompletionResponse(...) abort
    let b:ale_completion_result = ['foo']
  endfunction

After:
  unlet! b:ale_completion_info
  unlet! b:ale_completion_result
  unlet! b:lsp_started

  delfunction SetCompletionResult
  delfunction SetCompletionResponse

  runtime autoload/ale/lsp_linter.vim

  call ale#linter#Reset()

Given typescript():
  let abc = y.
  let foo = ab
  let foo = (ab)

Execute(-3 should be returned when completion results cannot be requested):
  AssertEqual -3, ale#completion#OmniFunc(1, '')

Execute(The start position should be returned when results can be requested):
  let b:lsp_started = 1
  call setpos('.', [bufnr(''), 3, 14, 0])

  AssertEqual 11, ale#completion#OmniFunc(1, '')

Execute(The omnifunc function should return async results):
  " Neovim struggles at running these tests.
  if !has('nvim')
    call timer_start(0, function('SetCompletionResult'))

    AssertEqual ['foo'], ale#completion#OmniFunc(0, '')
  endif

Execute(The omnifunc function should parse and return async responses):
  if !has('nvim')
    call timer_start(0, function('SetCompletionResponse'))

    AssertEqual ['foo'], ale#completion#OmniFunc(0, '')
  endif