stream, test: add tests for _readableStream.awaitDrain

@Fishrock123

Part of #8644.

The _readableState that needs to be tested is:

stream._readableState.awaitDrain

node/lib/_stream_readable.js

Lines 88 to 89 in 774146d

    
           // the number of writers that are awaiting a drain event in .pipe()s 
        
           this.awaitDrain = 0;

.

See also #8683

cc @Fishrock123 @nodejs/streams

I have made a proposal how this state variable can be tested in PR #8914 .
As we already have some tests for awaitDrain - I think it's better to add some asserts to them for covering real awairDrain value.
Also tests now cover reseting awaitDrain counter.
But I don't understand what this test is doing and can't rewrite it correctly. Can you someone help me with that?

@shmuga

@shmuga yes, good job!

The test you mentioned is increasing the awaitDrain mechanism manually, by calling resume: https://github.com/nodejs/node/blob/master/test/parallel/test-stream-pipe-await-drain-manual-resume.js#L29-L34.
You need to check that awaitDrain gets increased.

On that test, you should basically check that awaitDrain goes to zero as describe in: https://github.com/nodejs/node/blob/master/test/parallel/test-stream-pipe-await-drain-manual-resume.js#L37-L40

@mcollina

@mcollina great. will add some more tests for manual-resume. But I think this comment

// First pause, resume manually. The next write() to writable will still
// return false, because chunks are still being buffered, so it will increase
// the awaitDrain counter again.

is a bit strange at the place "increase again".
As we have only one writer here - the counter can't be increased more than one time.
So probably I will change that comment.

@shmuga

@shmuga resume interacts with awaitDrain: https://github.com/nodejs/node/blob/master/lib/_stream_readable.js#L741

See also https://github.com/nodejs/node/blob/master/lib/_stream_readable.js#L556.

When was that test added? Who did it? It might be worth getting the original PR here, and discussing with the author.

@mcollina

@mcollina I found nice description of this test in commit e2e615e

I will just follow those instructions and add cover tests for awaitDrain state variable.

Closed by 21a077a

test: tests for _readableStream.awaitDrain

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stream, test: add tests for _readableStream.awaitDrain #8684

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	// the number of writers that are awaiting a drain event in .pipe()s
	this.awaitDrain = 0;

stream, test: add tests for _readableStream.awaitDrain #8684

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shmuga commented on Oct 3, 2016

mcollina commented on Oct 3, 2016

shmuga commented on Oct 3, 2016

mcollina commented on Oct 3, 2016

shmuga commented on Oct 4, 2016

mcollina commented on Jan 18, 2017

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