assert: adds rejects() and doesNotReject()

[feugy]

Implement async equivalent of assert.throws() and assert.doesNotThrow().

This PR is a follow-up of #17843, but takes into account James' suggestion to bring this as experimental feature, without change the existing API.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

assert

[joyeecheung]

Nit: s/conveniency/convenience/?

[feugy]

Thank you 😅

[joyeecheung]

Maybe name assert.doesNotThrow as a top level function and reference it directly here to avoid being messed up by monkey-patched assert.doesNotThrow

[joyeecheung]

Maybe name assert.throws as a top level function and reference it directly here to avoid being messed up by monkey-patched assert.throws

[feugy]

👌

[joyeecheung]

Since other assigned APIs do not return promises here:

require('assert').promises.fail().then(()=>{});// does not work

This behavior looks somewhat strange to me..

[BridgeAR]

To me as well. I would rather have a dedicated assert.rejects function. Reject is used for promises, so this is a good fit out of my perspective.

[feugy]

That's an interesting point.

My intention was to keep the existing behaviour for all assert functions except throws() and doesNotThrow(), which are the only two able to run (potentially async) code.
I wouldn't like to force people writing:

constassert=require('assert').promisesawaitassert(something)

But we can definitely add new functions like reject() that would be async equivalent of existing one.
Are there any other function you would like to cover?

[joyeecheung]

If we are not talking about redesigning a new assert API here, providing a promisified version of the existing assert APIs is good enough to me. Something like

for(constkeyofObject.keys(assert)){constsyncFunc=assert[key];promises[key]=asyncfunction(...args){returnsyncFunc(...args)};}// override throws later, or in the block

[feugy]

hum, but it's actually what I'd like to avoid.

There's no point making assert.ok() or assert.fail() asynchronous. It will make the API more cumbersome to use with no benefit.

It make sense for assert.throws() and assert.doesNotThrow() to turn this code (that we used quite a lot in our projects):

it('should report database option errors',async()=>{try{awaittransferData({},'');thrownewError('it should have failed');}catch(err){assert(err.message.includes('"host" is required'));}});

into

it('should report database option errors',async()=>assert.throws(async()=>transferData({},''),/^Error:"host"isrequired/));

I don't want to redesign the whole API, but rather wants to support the above.

[BridgeAR]

Why not?

[feugy]

In this PR, you have currently (all synchronous):

• require('assert').equal
• require('assert').strict.equal
• require('assert').promises.equal
• require('assert').promises.strict.equal

I wasn't sure it worth providing require('assert').strict.promises. Do you think it worth it?

[BridgeAR]

In general strict and regular assert should have exactly the same API.

[feugy]

Copy that

[BridgeAR]

To me as well. I would rather have a dedicated assert.rejects function. Reject is used for promises, so this is a good fit out of my perspective.

[BridgeAR]

Because there seems to be a bit of confusion in the discussion:

I personally am strongly against adding a new promise API.

The only thing that should be added out of my perspective are two new functions rejects and doesNotReject. These two would be accessible in both the legacy and strict mode.

They behave similar to the current throws and doesNotThrow functions but they are async instead of sync. No other assert function should be async as there is no reason for it as far as I can tell.

[feugy]

@BridgeAR, by bringing assert.promises, I was following the advise @jasnell gave me on my previous PR.

But what you suggested above makes more sense, so I'm 100% with you, and implement it if @joyeecheung is happy with it.

[joyeecheung]

@feugy If adding asynchronous versions of the synchronous APIs doesn't make sense, then maybe we don't even need to add them to assert.promises. It's fine to only have throws() and doesNotThrow() in assert.promises, and we can work out other APIs later. IMO assert.promises don't need to be feature-complete in this PR.

[apapirovski]

This is a good start but I'm also in favour of using rejects and doesNotReject instead of a separate promises namespace.

(Worth noting that this would also be in line with the fact that promises emit unhandledRejection rather than uncaughtException.)

[apapirovski]

Can this be moved down closer to trySyncBlock which is its first usage? Or otherwise, move up those two functions here.

I would actually even suggest just inlining this function since it's only used twice. The savings are minimal and now the error thrown will have an extra function in the trace. The latter can be worked around (captureStackTrace) but I don't think it's worth it.

[apapirovski]

We don't need the common.platformTimeout here. Just matters that it's async.

[apapirovski]

nits:
s/doNotThrows()/doesNotThrow()
s/truely/truly
s/other/others

[apapirovski]

s/or let it bubble/or rethrow.

[apapirovski]

catch (err) or catch (e) is more in line with other usage in the code base.

[feugy]

Hello gents!

What do you think about the latest update?

[jasnell]

LGTM if CI is green

[jasnell]

Hello gents!

quick fyi... we're not all "gents" :-)

[feugy]

Sorry, it's bad habit 😓
I'll start documenting the new functions then.

[BridgeAR]

Overall it is already looking very promising to me! Just a few small comments :-)

[BridgeAR]

This is actually a slightly different behavior as before.

Before assert.throws(() =>{}, 'foo', undefined) would also result in an error. That is not the case anymore with this change. As this is completely independent from the actual change here, I would rather not have this included, especially as I think this should throw.

[feugy]

You're absolutely right!

To keep this code in an internal function, and not break the existing behaviour, I've used rest params and splat so arguments.length would still make sense.

[BridgeAR]

The comment is actually not correct anymore as it is only a no-op in case actual is the sentinel.

I personally feel like it is not necessary to have these comments here because the code is easy to understand but others might disagree.

[feugy]

👌

[BridgeAR]

Super tiny nit:

Destructuring would be nice as in const{promisify } = require('util')

[BridgeAR]

I am not totally happy with this test as it does not test that the code does not fail sync.

So I would write something like:

assert.doesNotThrow(()=>{assert.rejects(()=>assert.fail(),common.expectsError({code: 'ERR_ASSERTION',type: assert.AssertionError,message: 'Failed',operator: undefined,actual: undefined,expected: undefined}))});

The same applies to the test below.

[feugy]

👌

[BridgeAR]

If I am not mistaken, we do not know if these really work because the function itself might theoretically execute sync.

So a better test out of my perspective would be:

letpromise;letthrew=false;try{promise=assert.doesNotReject(async()=>{awaitwait(10);assert.fail();});}catch(err){threw=true;}assert.strictEqual(threw,false);assert.rejects(()=>promise,common.expectsError({code: 'ERR_ASSERTION',type: assert.AssertionError,message: 'Got unwanted exception ... '...}));

[feugy]

👌

[BridgeAR]

Hm, I would say it tests the functionality of assert.rejects() and assert.doesNotReject() but not that it "ensures" async support for those as they should always be async.

I would describe it as e.g. "Tests assert.rejects() and assert.doesNotReject() by checking their expected output and by verifying that they do not work sync."

[BridgeAR]

I am a bit surprised that this for the stackStartFn shall work. this should normally refer to either assert.ok or assert.strict.
Can you please write a test for this as well if none exist? :-)

[feugy]

I added a test, and you were absolutely right.
Providing explicit values keeps the existing stack-traces:

https://github.com/feugy/node/blob/6cdbbe6f520862edda962dbf8507c9e7917bdd1e/test/parallel/test-assert-async.js#L60-L98

[BridgeAR]

The code change itself looks very good now! Just the tests might need a bit more polishing :-)

[BridgeAR]

Super super tiny nit: you can actually access the own function without assert. It would just save some characters.

[joyeecheung]

It also keep you away from monkey-patching. I would prefer referencing it directly here.

[BridgeAR]

Nit: It would be really nice if the error message is changed to Missing expected rejection.

[BridgeAR]

The two tests above are already tested for in test-assert.js. This adds the check for the error stack, so it indeed tests something new, but in that case I would rather replace the ones in test-assert.js with these tests instead of "duplicating" them.

[BridgeAR]

This tests the same as https://github.com/nodejs/node/pull/18023/files#diff-cdf49dc677a8ea6f00de9f95639355e8R44.
What was not yet tested for is if the functions throws sync.

[BridgeAR]

Using a async function as wrapper will actually hide if the function is executed sync or async. So I would just use the pattern as above without the async wrapper.

[BridgeAR]

@feugy thanks a lot for being so patient!

[Leko]

LGTM

[joyeecheung]

It also keep you away from monkey-patching. I would prefer referencing it directly here.

[joyeecheung]

LGTM with @BridgeAR 's comments addressed

[feugy]

Maybe the next lines (copied from assert.doesNotThrow() doc) may be skipped in favour of a reference?

[BridgeAR]

I agree. I would actually even go so far and remove everything from here on. A text like:

Besides the async nature to await the completion it behaves identical to `assert.doesNotThrow()`.

Keep an example with async await and also maybe add a example using promises.

The same can be applied to the reject function.

[feugy]

operator & message will now contain appropriate values

[BridgeAR]

There is the unwritten rule to not use multi line template strings in Node.js. This does look somewhat elegant but it is probably best to just have something like: Missing expected ${fnType}${details}.

[feugy]

I wasn't confident to replace common.expectsError() with such custom assertions, but couldn't find a better way to reuse the existing test, as suggested.

[BridgeAR]

I would actually just keep this as is and just add a single line to one of the existing tests that checks for assert.ok(!err.stack.includes('at throws').

[BridgeAR]

This exceeds 80 characters.

[BridgeAR]

Nit (non-blocking): I personally prefer the following to save lines:

assert.throws=functionthrows(block, ...args){expectsError(throws,getActual(block), ...args);};

[feugy]

I also prefer function expressions.
But even named, function expression do not benefit from hoisting.

This would imply to use assert.doesNotReject()here, and here.

Same goes for other functions.

[BridgeAR]

Good point. We could check for the function name instead but that could theoretically be manipulated.

So just keep it as is. Thanks for the heads up.

[BridgeAR]

Hm, while looking at the code again: we actually already use the function name and do not strictly test if it it a "valid" function. So we could indeed just switch to name checking only.

[BridgeAR]

I agree. I would actually even go so far and remove everything from here on. A text like:

Besides the async nature to await the completion it behaves identical to `assert.doesNotThrow()`.

Keep an example with async await and also maybe add a example using promises.

The same can be applied to the reject function.

[BridgeAR]

There is the unwritten rule to not use multi line template strings in Node.js. This does look somewhat elegant but it is probably best to just have something like: Missing expected ${fnType}${details}.

[BridgeAR]

I am relatively certain that this is going to trigger a lint error. The err should probably be in parentheses. The same applies to the test below.

[BridgeAR]

After thinking about this again, the try catch and the threw is not necessary here at all. If the promise throws the test would fail right away. threw is only necessary for tests that check for threw === true. So the tests can be much smaller (I know I originally suggested this pattern).

[BridgeAR]

The wrapper is not needed as the test would fail right away if assert.rejects would fail.

[BridgeAR]

The wrapper is not needed due to the reason mentioned above.

[BridgeAR]

I would actually just keep this as is and just add a single line to one of the existing tests that checks for assert.ok(!err.stack.includes('at throws').

[BridgeAR]

Hm, I am not certain if that is actually true? I thought that frame would actually be excluded? Do the tests pass?

[BridgeAR]

@feugy see #18699 and #18669.

I would just wait with removing it until it is decided if we deprecate it or not because I would like to have feature parity.

[apapirovski]

@BridgeAR It seems to me like rejections have slightly different semantics than throw. Since it's currently possible to just entirely ignore unhandledRejection in our code, I can see a use for doesNotReject. Just IMO of course...

[BridgeAR]

@apapirovski I agree that it is not exactly the same but the reason for that is that we have another issue that has to be solved as well. See #15126.

[apapirovski]

@BridgeAR Yeah, I'm aware and have dug around in that PR, actually, but that code will take a while to land given the performance implications. I'm not really certain we have a great path forward that doesn't impact performance. Maybe I'm wrong...

(I have some thoughts on how to do it without all of the C++ boundary crossing but only theoretical atm.)

[apapirovski]

@BridgeAR given that this is only semver-minor whereas any changes to uncaught Promise handling would be semver-major, do you think it would be ok to land as is? Especially in the light of the recent rejection of the doesNotThrow deprecation?

[apapirovski]

CI: https://ci.nodejs.org/job/node-test-pull-request/13496/

[BridgeAR]

@apapirovski yes, I am now ok with landing it as is. I will open another PR to add a comment to it similar to doesNotThrow afterwards.

@feugy thanks a lot for your work and for being patient :)

[feugy]

It's all fine!
I'll resolve the conflict soon.

[feugy]

And done! What's next?

[BridgeAR]

Landed in 599337f 🎉

I removed the experimental as I do not really see that and fixed a typo in the docs while landing.

[MylesBorins]

Should this be backported to v9.x-staging? If yes please follow the guide and raise a backport PR, if not let me know or add the dont-land-on label.

[not-an-aardvark]

If this gets backported, it should be backported at the same time as #19650 (possibly in the same commit).