question: best practice for handling unexpected `err` in tests

[refack]

• Version: master
• Platform: *
• Subsystem: test

Ref: #13092 (comment)
Do we have a better construct for handling err in callbacks:
What I found that gives the most informative results (stack of exception and a frame for the test) are:

• for regular callbacks common.mustCall((err) => {if (err) assert.fail(err)})
• for .on('error') handlers (err) => assert.fail(err)

That is the only way to get a frame in the stack.

regular callback

common.mustCall((err) => {if (err) assert.fail(err)})

AssertionError [ERR_ASSERTION]: Error: ENOENT: no such file or directory, open 'd:\code\node-cur\test\tmp\watch\foo.txt?'
    at fs.writeFile.common.mustCall (d:\code\node-cur\test\parallel\test-fs-watchfile.js:79:86)
    at d:\code\node-cur\test\common\index.js:504:15
    at fs.js:1239:7
    at FSReqWrap.oncomplete (fs.js:112:15)

with common.mustCall((err) => {assert.ifError(err)})

or common.mustCall(assert.ifError)

assert.js:574
assert.ifError = function ifError(err) { if (err) throw err; };
                                                  ^

Error: ENOENT: no such file or directory, open 'd:\code\node-cur\test\tmp\watch\foo.txt?'

.on('error')

with (err) => assert.fail(err)

assert.js:92
  throw new AssertionError({
  ^

AssertionError [ERR_ASSERTION]: Error: write EPROTO 101057795:error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol:openssl\ssl\s23_clnt.c:794:

    at ClientRequest.req.on (D:\code\node-cur\test\parallel\test-async-wrap-GH13045.js:63:35)
    at emitOne (events.js:115:13)
    at ClientRequest.emit (events.js:210:7)
    at TLSSocket.socketErrorListener (_http_client.js:397:9)
    ...

with just assert.fail

assert.js:92
  throw new AssertionError({
  ^

AssertionError [ERR_ASSERTION]: Error: write EPROTO 101057795:error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol:openssl\ssl\s23_clnt.c:794:

    at emitOne (events.js:115:13)
    at ClientRequest.emit (events.js:210:7)
    at TLSSocket.socketErrorListener (_http_client.js:397:9)
    ...

[refack]

/cc @nodejs/testing

[Trott]

I think what you wrote above is a pretty good summary. Some stuff may have changed, I'm not sure, but you probably know because you're probably the person that would have changed it :-D

If you think it belongs in the test-writing guide, by all means, go for it. Lint rules might be feasible too, not sure to be honest. I'm going to close, but feel free to re-open if there's more to talk about.

[refack]

Yeah, time to turn this into action.