test: proc.on('close') event

[justinmk]

This is a demo for a potential issue noticed in #419 / #414 (comment)

Problem

proc.on('close') does not always trigger on nvim.quit(). Based on the failures from the test changes in this PR, it appears that sometimes the child (nvim) does not close the stderr pipe:

    expect(received).toStrictEqual(expected) // deep equality

    - Expected  - 1
    + Received  + 1

      Object {
        "errors": 0,
    -   "stderrClosed": true,
    +   "stderrClosed": false,
        "stdoutClosed": true,
      }

      172 |     // TODO: 'close' event sometimes does not emit. #414
      173 |     proc.on('exit', () => {
    > 174 |       expect(r).toStrictEqual({
          |                 ^
      175 |         stdoutClosed: true,
      176 |         stderrClosed: true,
      177 |         errors: 0,

      at ChildProcess.toStrictEqual (src/attach/attach.test.ts:174:17)

Solution

This seems like a potential bug or at least something to document in Nvim itself. I thought it might be related to this: https://github.com/neovim/neovim/blob/c4762b309714897615607f135aab9d7bcc763c4f/src/nvim/channel.c#L168-L171

      // Don't close on exit, in case late error messages
      if (!exiting) {
        fclose(stderr);
      }

but, forcing fclose(stderr) does not pass the tests in this PR. Nor does adding fclose(stderr) anywhere else AFAICT.