Mock time

We should make sure that there is only one source of time in Textual.

Ideally App should have get_time function which returns the current time.

We should have a mechanism to replace the system time with an alternative time, which we can use to ensure tests are deterministic.

Suggest that App accepts a get_time callable which will replace monotonic

[willmcgugan]

I don’t think there is any performance issue in getting the time, it’s a fairly lean operation:

>>> monotonic()-monotonic()
-1.1669471859931946e-06

I think I see where you are going with an orchestrator. I hadn’t considered asyncio.sleep as a sneaky source of time that we can’t control.

But I suspect 60fps is going to be a performance drain. If I have understood you correctly, it would have to be running all the time. Even if it wasn’t doing anything, thats still a cpu drain.

How about we move all explicit calls to get the time in to app, which we can mock. We also move the responsibility for asyncio.sleep in to App. In normal operation we defer to asyncio.sleep, but for testing we base it on our mocked time.

I’m thinking a method like App.advance_time(delta) which moves the clock forward and wakes up any sleeping cooroutines.

Let’s have a chat about it tomorrow. It’s a tricky topic, and it’s worth having the 3 of us on this.

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