Before:
  Save g:ale_use_neovim_diagnostics_api

  function! CollectMessages(buffer)
    if !has('nvim-0.6')
        return
    endif

    let l:messages = []
    for l:diag in v:lua.vim.diagnostic.get(a:buffer)
        call add(l:messages, l:diag.message)
    endfor

    return l:messages
  endfunction


After:
  unlet! b:other_bufnr
  delfunction CollectMessages
  Restore

Execute(Should only set diagnostics belonging to the given buffer):
  if has('nvim-0.6')

  let b:other_bufnr = bufnr('/foo/bar/baz', 1)
  " Make sure we actually get another buffer number, or the test is invalid.
  AssertNotEqual -1, b:other_bufnr

  let g:ale_use_neovim_diagnostics_api = 1

  call ale#engine#SetResults(bufnr('%'), [
  \  {
  \    'lnum': 1,
  \    'col': 10,
  \    'bufnr': bufnr('%'),
  \    'vcol': 0,
  \    'linter_name': 'bettercode',
  \    'nr': -1,
  \    'type': 'W',
  \    'text': 'A',
  \  },
  \  {
  \    'lnum': 2,
  \    'col': 10,
  \    'bufnr': b:other_bufnr,
  \    'vcol': 0,
  \    'linter_name': 'bettercode',
  \    'nr': -1,
  \    'type': 'W',
  \    'text': 'B',
  \  },
  \  {
  \    'lnum': 3,
  \    'col': 1,
  \    'bufnr': bufnr('%'),
  \    'vcol': 0,
  \    'linter_name': 'bettercode',
  \    'nr': -1,
  \    'type': 'E',
  \    'text': 'C',
  \  },
  \  {
  \    'lnum': 4,
  \    'col': 1,
  \    'bufnr': b:other_bufnr,
  \    'vcol': 0,
  \    'linter_name': 'bettercode',
  \    'nr': -1,
  \    'type': 'E',
  \    'text': 'D',
  \  },
  \])

  AssertEqual ["A", "C"], CollectMessages(bufnr('%'))

  endif