Before:
  Save g:ale_buffer_info
  Save &filetype
  Save g:ale_set_lists_synchronously

  let g:ale_set_lists_synchronously = 1

  " Set up items in other buffers which should set in this one.
  let g:ale_buffer_info = {}
  call ale#engine#InitBufferInfo(bufnr('') + 1)
  let g:ale_buffer_info[bufnr('') + 1].loclist =
  \ ale#engine#FixLocList(bufnr('') + 1, 'linter_one', 0, [
  \   {'lnum': 1, 'filename': expand('%:p'), 'text': 'foo'},
  \   {'lnum': 2, 'filename': expand('%:p'), 'text': 'bar'},
  \   {'lnum': 2, 'text': 'ignore this one'},
  \ ])
  call ale#engine#InitBufferInfo(bufnr('') + 2)
  let g:ale_buffer_info[bufnr('') + 2].loclist =
  \ ale#engine#FixLocList(bufnr('') + 2, 'linter_one', 0, [
  \   {'lnum': 1, 'filename': expand('%:p'), 'text': 'foo'},
  \   {'lnum': 3, 'filename': expand('%:p'), 'text': 'baz'},
  \   {'lnum': 5, 'text': 'ignore this one'},
  \ ])

  call ale#linter#Define('foobar', {
  \ 'name': 'linter_one',
  \ 'callback': 'WhoCares',
  \ 'executable': 'echo',
  \ 'command': 'sleep 1000',
  \ 'lint_file': 1,
  \})

After:
  call ale#engine#Cleanup(bufnr(''))
  Restore
  call ale#linter#Reset()

  " Items and markers, etc.
  call setloclist(0, [])
  call clearmatches()
  call ale#sign#Clear()

Given foobar(A file with some lines):
  foo
  bar
  baz

Execute(Problems found from previously opened buffers should be set when linting for the first time):
  call ale#engine#RunLinters(bufnr(''), ale#linter#Get(&filetype), 0)

  AssertEqual
  \ [
  \   {
  \     'lnum': 1,
  \     'bufnr': bufnr(''),
  \     'col': 0,
  \     'filename': expand('%:p'),
  \     'linter_name': 'linter_one',
  \     'nr': -1,
  \     'type': 'E',
  \     'vcol': 0,
  \     'text': 'foo',
  \     'sign_id': 1000001,
  \   },
  \   {
  \     'lnum': 2,
  \     'bufnr': bufnr(''),
  \     'col': 0,
  \     'filename': expand('%:p'),
  \     'linter_name': 'linter_one',
  \     'nr': -1,
  \     'type': 'E',
  \     'vcol': 0,
  \     'text': 'bar',
  \     'sign_id': 1000002,
  \   },
  \   {
  \     'lnum': 3,
  \     'bufnr': bufnr(''),
  \     'col': 0,
  \     'filename': expand('%:p'),
  \     'linter_name': 'linter_one',
  \     'nr': -1,
  \     'type': 'E',
  \     'vcol': 0,
  \     'text': 'baz',
  \     'sign_id': 1000003,
  \   },
  \ ],
  \ g:ale_buffer_info[bufnr('')].loclist

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