If I can t use the SystemClock in my unit tests then what s

Question

If I can t use the SystemClock in my unit tests then what s the point of the time value in `advanceTimeBy` For example I m using a fake timesource so the actual advanced time doesn t matter

hfhbd · Answer

What do you mean This ```runTest advanceTimeBy 1 minutes ```

Florian Walther (live streaming) · Answer

yes

Florian Walther (live streaming) · Answer

I need to use it to execute code but the actual value in there doesn t seem to matter

Florian Walther (live streaming) · Answer

because the time is coming from my fake time source

hfhbd · Answer

Are you using `TestScope` with another TimeSource not the provided one

hfhbd · Answer

This is the idea using the provided `testTimeSource` ``` Test ExperimentalTime fun testAdvanceTimeSource = runTest val expected = 1 seconds val actual = testTimeSource measureTime delay expected or advanceTimeBy 1 seconds assertEquals expected actual ```

hfhbd · Answer

See also <https github com Kotlin kotlinx coroutines issues 3086>

Florian Walther (live streaming) · Answer

What exactly is `timeSource` I don t have that available in my code

Florian Walther (live streaming) · Answer

False alarm I have it available I didn t know about this thank you So I should use this instead of my own fake time source right

Florian Walther (live streaming) · Answer

This doesn t seem to be mentioned in the `kotlinx coroutines test` documentation Where do I learn about this stuff

Florian Walther (live streaming) · Answer

But how do I use this in my own classes I wanna uses the `SystemClock` s `elapsedRealtime` in my production code

hfhbd · Answer

Yes you should could use this timeSource slightly smiling face What is SystemClock

Florian Walther (live streaming) · Answer

oh SystemClock is an Android class

Florian Walther (live streaming) · Answer

Should I wrap this in my own TimeSource interface

Florian Walther (live streaming) · Answer

I m using the SystemClock s time to make my countdown timer exact delay itself isn t Is Kotlin s TimeSource exact

Florian Walther (live streaming) · Answer

When I use TimeSource Monotonic on Android I m always getting 0 for `elapsedNow`

hfhbd · Answer

First TimeSource is not a Clock TimeSource Monotonic is only usable for jobs with keeping your system active Its behavior is not defined when your computer sleeps or it does not support NTP update See details here <https github com Kotlin kotlinx datetime pull 164 issuecomment 997859203> Oh SystemClock is a final class without an interface How do you mock it at all For tests you increase the timesource by your own So you are safe to write some kind `TimeSource toTestSystemClock ` In tests `delay` is exact

Florian Walther (live streaming) · Answer

i need an exact time source in my production code so the timer works

Florian Walther (live streaming) · Answer

that s why I use Android s SystemClock for reference

Florian Walther (live streaming) · Answer

But in my tests the time is coming from my own fake time source wrapper

Florian Walther (live streaming) · Answer

it s just that the `TestScope` s time doesn t really mean anything anymore

Florian Walther (live streaming) · Answer

it just has to be enough to skip delays

hfhbd · Answer

but how do you mock SystemClock

Florian Walther (live streaming) · Answer

I have a wrapper that uses the SystemClock in real code and a Long value in the tests

Florian Walther (live streaming) · Answer

in the fake on I have an advance time method that i use to increase that Long

hfhbd · Answer

Okay if you already use `Long` what prevents you from using `TestScope currentTime` smile

Florian Walther (live streaming) · Answer

I don t know what to use in my production code

Florian Walther (live streaming) · Answer

Especially since i need an exact reference point to avoid that the timer becomes imprecise