Before:
  let g:start = 0
  let g:success = 0
  let g:ale_run_synchronously = 1

  function! TestCallback(buffer, output)
    return [{
    \ 'lnum': 1,
    \ 'col': 3,
    \ 'text': 'baz boz',
    \}]
  endfunction

  call ale#linter#Define('foobar', {
  \ 'name': 'testlinter',
  \ 'callback': 'TestCallback',
  \ 'executable': has('win32') ? 'cmd' : 'true',
  \ 'command': has('win32') ? 'echo' : 'true',
  \})
  "let g:ale_linters = {'foobar': ['lint_file_linter']}

After:
  let g:ale_run_synchronously = 0
  let g:ale_buffer_info = {}
  let g:ale_linters = {}
  call ale#linter#Reset()
  delfunction TestCallback
  augroup! VaderTest

Execute (Run a lint cycle, and check that a variable is set in the autocmd):
  set filetype=foobar
  augroup VaderTest
    autocmd!
    autocmd User ALEStartLint let g:start = 1
    autocmd User ALELint      let g:success = 1
  augroup end

  call ale#Lint()

  AssertEqual g:start, 1
  AssertEqual g:success, 1