I finally solved my Compose testing problems, afte...

# compose

[Tim Malseed]

I finally solved my Compose testing problems, after spending quite some time trying to track down some very obscure bugs!

With Compose, when testing screens, you call composeTestRule.setContent { MyScreen() }  - if you’ve written Compose UI tests, you’d be familiar with this.

If you need to run the tests against a particular activity, for some reason, you can use androidComposeTestRule<MyActivity>

In my case, MyActivity calls setContent { MyScreen() } during onCreate().

So, what ends up happening, is the test instantiates MyActivity, which calls setContent(), and the screen is composed, with its ViewModel and various dependencies. While this is happening, the test calls its own setContent() and the screen is composed again, in parallel! This causes all kinds of nightmarish problems.

tl;dr

Make sure when testing Compose, that you only call setContent() once per test. And be careful about which Activity you use to host the test, if you need one!

[Colton Idle]

oof. so if my activity already calls setContent, I shouldnt call setContent in my test, right?

[Tim Malseed]

If your test uses androidComposeTestRule, and so runs inside an Activity that already calls setContent(), then calling setContent() again in your test can cause issues.

[Tim Malseed]

So, my advice isn’t ‘don’t call setContent() in test’. But rather, don’t test against an Activity that calls setContent()

My solution was to create another Activity just for test purposes. And, to keep this from prod, I only declare this Activity in the debug AndroidManifest

[Alex Vanyo]

If you don’t need a specific Activity, you can use a plain createComposeRule() instead along with the ui-test-manifest dependency. If you add it with debugImplementation, this should function exactly like your test activity:

debugImplementation("androidx.compose.ui:ui-test-manifest:$compose_version")

[Tim Malseed]

Yep. This issue only occurs when you do need a specific Activity, like when you’re injecting stuff via Hilt

[Colton Idle]

Yeah, I think I need a specific activity because I'm trying to create a few (like 5) critical path end to end tests. So I actually want it to start my app and just assert some basic things.

[Colton Idle]

And so therefore, my end to end test, wouldn't need to call set content, since the activity already calls setConent

[Tim Malseed]

Yeah. But, when you want to test a Composable in isolation - that’s when you want to be able to call setContent()

[Tim Malseed]

So there’s like, this very specific set of circumstances that can lead to a lot of pain 😭

[Colton Idle]

"So there’s like, this very specific set of circumstances that can lead to a lot of pain"

I think you've summed up software engineering.