ProcessLifecycleOwner/Robolectric issues

This is a sample project demonstrating issues with robolectric unit tests and the ProcessLifecycleOwner.

Background:

In an app, the ProcessLifecycleOwner hooks into activity lifecycles and reports on the global lifecycle of the application (simplified summary: if any activity is resumed, the process lifecycle is RESUMED, if no activities have been launched, the process lifecycle is CREATED...). An application may rely on ProcessLifecycleOwner if it has logic to not execute a particular task unless the app has at least one visible activity, for example.

In an app, the ProcessLifecycleOwner is registered in a <provider> called ProcessLifecycleOwnerInitializer. This provider snippet in the manifest is generated by the build tools. In robolectric tests, this provider isn't launched by default.

The first hack is to "install" the ProcessLifecycleOwner class: make it so that this singleton will hook into activity lifecycles and correctly report on the overall lifecycle of the application. This could be done by registering the ProcessLifecycleOwnerInitializer content provider with robolectric, or by executing the same code the ProcessLifecycleOwnerInitializer itself does. Our hacky ProcessLifecycleTrojan class does the latter, in its setup() function.

ProcessLifecycleOwner is a singleton, and thus maintains a static state across tests. The second hack is to use reflection to make sure we have a fresh new instance of ProcessLifecycleOwner for each test, by resetting its static sInstance field, in ProcessLifecycleTrojan.tearDown().

This second hack no longer works in Robolectric 4.3. It fails with this exception:

java.lang.IllegalAccessException: Can not set static final androidx.lifecycle.ProcessLifecycleOwner field androidx.lifecycle.ProcessLifecycleOwner.sInstance to androidx.lifecycle.ProcessLifecycleOwner

	at sun.reflect.UnsafeFieldAccessorImpl.throwFinalFieldIllegalAccessException(UnsafeFieldAccessorImpl.java:76)
	at sun.reflect.UnsafeFieldAccessorImpl.throwFinalFieldIllegalAccessException(UnsafeFieldAccessorImpl.java:80)
	at sun.reflect.UnsafeQualifiedStaticObjectFieldAccessorImpl.set(UnsafeQualifiedStaticObjectFieldAccessorImpl.java:77)
	at java.lang.reflect.Field.set(Field.java:764)
	at androidx.lifecycle.ProcessLifecycleTrojan.tearDown(ProcessLifecycleTrojan.kt:61)
	at com.example.processlifecycleownerpersistedstate.ExampleUnitTest.tearDown(ExampleUnitTest.kt:29)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:33)

Problem details:

Steps to reproduce the various issues:

Problem 1: ProcessLifecyleOwner not setup: not reporting resumed state for a resumed activity

• Keep robolectric 4.2.1 (default in this project)
• Comment out the setup() and tearDown() functions in ExampleUnitTest, to not use the ProcessLifecycleTrojan hack at all.
• Run the tests.
• Expected behavior: the tests pass.
• Actual behavior:
  • The tests fail as the first assertion that the state should be CREATED (it's in fact INITIALZED)
  • Comment out that first assertion, and the second assertion fails: We expect the state to be RESUMED but it's INITIALIZED still.

Problem 2: ProcessLifecycleOwner setup, but not reset after each test

• Keep robolectric 4.2.1 (default in this project)
• Keep the ExampleUnitTest.setup() function to hook ProcessLifecycleOwner into activity lifecycles
• Comment out the ExampleUnitTest.tearDown() function to remove the reflection hack that resets the ProcessLifecycleOwner singleton.
• Comment out the last three lines of ExampleUnitTest.testLaunchActivity() which destroy the activity
• Run the tests.
• Expected behavior: the tests pass
• Actual behavior:
  • testLaunchActivity1() passes, but testLaunchActivity2() fails. Its first assertion fails: We expect the app state to be CREATED, but it's RESUMED (left over from the first test).

Problem 3: Can't reset the ProcessLifecycleOwner state for each test, with robolectric 4.3

• Update to robolectric 4.3
• Put back any lines you have have commented out while testing the previous problems.
• Run the tests.
• Expected behavior: the tests pass
• Actual behavior: IllegalAccessException in ProcessLifecycleTrojan.tearDown()

This problem is avoided by using ReflectionHelpers.callConstructor() and ReflectionHelpers.setStaticField().