Before:
  Save &filetype

  let g:queue_calls = []

  unlet! b:ale_lint_on_enter

  function! ale#Queue(...)
    call add(g:queue_calls, a:000)
  endfunction

After:
  Restore

  unlet! b:ale_lint_on_enter
  unlet! g:queue_calls

  " Reload the ALE code to load the real function again.
  runtime autoload/ale.vim

  unlet! b:ale_original_filetype

Execute(The original filetype should be set on BufEnter):
  let &filetype = 'foobar'

  call ale#events#EnterEvent(bufnr(''))

  AssertEqual 'foobar', b:ale_original_filetype

  let &filetype = 'bazboz'

  call ale#events#EnterEvent(bufnr(''))

  AssertEqual 'bazboz', b:ale_original_filetype

Execute(Linting should not be queued when the filetype is the same):
  let b:ale_original_filetype = 'foobar'
  let g:queue_calls = []

  call ale#events#FileTypeEvent(bufnr(''), 'foobar')

  AssertEqual [], g:queue_calls

Execute(Linting should be queued when the filetype changes):
  let b:ale_original_filetype = 'foobar'
  let g:queue_calls = []

  call ale#events#FileTypeEvent(bufnr(''), 'bazboz')

  AssertEqual [[300, 'lint_file', bufnr('')]], g:queue_calls

Execute(Linting shouldn't be done when the original filetype was blank and linting on enter is off):
  let b:ale_lint_on_enter = 0
  let b:ale_original_filetype = ''

  call ale#events#FileTypeEvent(bufnr(''), 'bazboz')

  AssertEqual [], g:queue_calls

Execute(Linting should be done when the original filetype was blank and linting on enter is on):
  let b:ale_lint_on_enter = 1
  let b:ale_original_filetype = ''

  call ale#events#FileTypeEvent(bufnr(''), 'bazboz')

  AssertEqual [[300, 'lint_file', bufnr('')]], g:queue_calls

Execute(The new filetype should become the "original" one if the original was blank and linting on enter is off):
  let b:ale_lint_on_enter = 0
  let b:ale_original_filetype = ''

  call ale#events#FileTypeEvent(bufnr(''), 'bazboz')

  AssertEqual 'bazboz', b:ale_original_filetype