Before:
  function! TestCallback(buffer, output)
    return [{
    \ 'lnum': 2,
    \ 'col': 3,
    \ 'text': a:output[0],
    \}]
  endfunction
  function! TestCallback2(buffer, output)
    return [{
    \ 'lnum': 3,
    \ 'col': 4,
    \ 'text': a:output[0],
    \}]
  endfunction

  " Running the command in another subshell seems to help here.
  call ale#linter#Define('foobar', {
  \ 'name': 'testlinter',
  \ 'callback': 'TestCallback',
  \ 'executable': 'echo',
  \ 'command': '/bin/sh -c ''echo foo bar''',
  \})

After:
  let g:ale_buffer_info = {}
  delfunction TestCallback
  delfunction TestCallback2
  call ale#linter#Reset()

Given foobar (Some imaginary filetype):
  foo
  bar
  baz

Execute(Linters should run with the default options):
  AssertEqual 'foobar', &filetype

  call ale#Lint()
  call ale#engine#WaitForJobs(2000)

  AssertEqual [{
  \   'bufnr': bufnr('%'),
  \   'lnum': 2,
  \   'vcol': 0,
  \   'col': 3,
  \   'text': 'foo bar',
  \   'type': 'E',
  \   'nr': -1,
  \   'pattern': '',
  \   'valid': 1,
  \ }], getloclist(0)

Execute(Previous errors should be removed when linters change):
  call ale#Lint()
  call ale#engine#WaitForJobs(2000)

  call ale#linter#Reset()

  call ale#linter#Define('foobar', {
  \ 'name': 'testlinter2',
  \ 'callback': 'TestCallback2',
  \ 'executable': 'echo',
  \ 'command': '/bin/sh -c ''echo baz boz''',
  \})

  call ale#Lint()
  call ale#engine#WaitForJobs(2000)

  AssertEqual [{
  \   'bufnr': bufnr('%'),
  \   'lnum': 3,
  \   'vcol': 0,
  \   'col': 4,
  \   'text': 'baz boz',
  \   'type': 'E',
  \   'nr': -1,
  \   'pattern': '',
  \   'valid': 1,
  \ }], getloclist(0)