Before:
  Save g:ale_use_neovim_diagnostics_api

  function! CollectMessages(buffer)
    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