Should just return self._when attribute.

I need it for testing purposes.
Without the method there is no possibility to figure out scheduled wakeup time.
An alternative is waiting for callback but the approach increases unittest execution time and not very reliable.

I don't like looking into `handler._when` private property, uvloop does not expose it.

Ned, is it possible to include the feature into Python 3.7? 
The change is safe and tiny, no backward compatibility problems etc.

How will such test look like? I'm still not sure we need it.

In aiohttp we have HTTP keepalivve support.

A function schedules a delayed callback.
On processing a new request the callback is cancelled and rescheduled to a new time.

I like to check cancellation state (now it is possible with public API) and scheduled time.

I did the check with mocking but proposed method allows to do it easy and more obviously.

OK, makes sense. Can you submit a PR?

Let's get it into master for 3.8 first and then we'll have something to discuss.

The PR is LGTM.  Up to Ned to allow this in 3.7.  I agree that the feature is (a) trivial, (b) new, so it's safe to go in 3.7.

> Let's get it into master for 3.8 first and then we'll have something to discuss.

The PR has a "versionadded" tag.  If you plan to allow this, Andrew can commit it set to 3.7...

We have feature freezes for a good reason.  But I will trust your judgement on this one. (Removing 3.6 for version list.)

Andrew, I'm indifferent about this feature.  It's entirely up to you if you want to merge it in 3.7.  I already used up my allowance for post-beta1 feature merges.

Thanks.
Let's do it.
The addition is really very trivial.