Make PaywallViewModel dispatcher injectable to fix flaky tests

[vegaro]

PaywallViewModelWorkflowTest looks flaky on CI

I believe the reason is that preWarmWorkflowStepCache() launches on viewModelScope (the test Main dispatcher) but hops to withContext(Dispatchers.Default) for the heavy computeStateForStep work.

Making the dispatcher injectable and injecting the test dispatcher in the workflow test's VM construction so the pre-warm runs on the test scheduler should fix it.

Example failure:

https://app.circleci.com/pipelines/github/RevenueCat/purchases-android/22653/workflows/97ebb0de-5850-4621-ae49-725e31304259/jobs/223710/tests

Failure in PaywallViewModelWorkflowTest

java.lang.IllegalStateException: Dispatchers.Main is used concurrently with setting it
	at kotlinx.coroutines.test.internal.TestMainDispatcher$NonConcurrentlyModifiable.concurrentRW(TestMainDispatcher.kt:72)
	at kotlinx.coroutines.test.internal.TestMainDispatcher$NonConcurrentlyModifiable.setValue(TestMainDispatcher.kt:90)
	at kotlinx.coroutines.test.internal.TestMainDispatcher.resetDispatcher(TestMainDispatcher.kt:41)
	at kotlinx.coroutines.test.TestDispatchers.resetMain(TestDispatchers.kt:34)
	at com.revenuecat.purchases.ui.revenuecatui.data.PaywallViewModelWorkflowTest.tearDown(PaywallViewModelWorkflowTest.kt:345)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
	at org.junit.internal.runners.statements.RunAfters.invokeMethod(RunAfters.java:46)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:33)
	at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:61)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.robolectric.RobolectricTestRunner$HelperTestRunner$1.evaluate(RobolectricTestRunner.java:524)
	at org.robolectric.internal.SandboxTestRunner.executeInSandbox(SandboxTestRunner.java:494)
	at org.robolectric.internal.SandboxTestRunner.access$900(SandboxTestRunner.java:67)
	at org.robolectric.internal.SandboxTestRunner$7.evaluate(SandboxTestRunner.java:442)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.robolectric.internal.SandboxTestRunner.access$600(SandboxTestRunner.java:67)
	at org.robolectric.internal.SandboxTestRunner$6.evaluate(SandboxTestRunner.java:333)
	at org.robolectric.internal.SandboxTestRunner$3.evaluate(SandboxTestRunner.java:233)
	at org.robolectric.internal.SandboxTestRunner$5.lambda$evaluate$0(SandboxTestRunner.java:317)
	at org.robolectric.internal.bytecode.Sandbox.lambda$runOnMainThread$0(Sandbox.java:101)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
	at java.base/java.lang.Thread.run(Thread.java:1583)
	Suppressed: org.robolectric.android.internal.AndroidTestEnvironment$UnExecutedRunnablesException: Main looper has queued unexecuted runnables. This might be the cause of the test failure. You might need a shadowOf(Looper.getMainLooper()).idle() call.

---

Note

Low Risk
Production behavior is unchanged thanks to the default dispatcher; only test construction and an internal injectable hook for pre-warm offloading.

Overview
Adds an optional backgroundDispatcher constructor parameter to PaywallViewModelImpl (default Dispatchers.Default) and uses it in preWarmWorkflowStepCache instead of a hardcoded Dispatchers.Default for computeStateForStep.

PaywallViewModelWorkflowTest passes the test StandardTestDispatcher so workflow step pre-warming stays on the test coroutine scheduler. That avoids work continuing on the real default pool after Dispatchers.resetMain(), which was causing flaky CI failures. Production wiring via PaywallViewModelFactory is unchanged and still uses the default dispatcher.

^{Reviewed by Cursor Bugbot for commit a99fef5. Bugbot is set up for automated code reviews on this repo. Configure here.}

[vegaro]

• Make PaywallViewModel dispatcher injectable to fix flaky tests #3544 👈 (View in Graphite)
• main

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.11%. Comparing base (e1de6c8) to head (a99fef5).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3544   +/-   ##
=======================================
  Coverage   80.11%   80.11%           
=======================================
  Files         371      371           
  Lines       15166    15166           
  Branches     2100     2100           
=======================================
  Hits        12150    12150           
  Misses       2166     2166           
  Partials      850      850           

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[facumenzella]

There isn't any clear way to make sure this addresses the flamines right? It would be great to link the failures to the PR description, so we can track this back

[vegaro]

added the failures @facumenzella