Suggestions for porting InstantTaskExecutorRule?

[autonomousapps]

JUnit5 does not support Rules. Yet some tests, particularly Android tests, absolutely require Rules. One example is the InstantTaskExecutorRule required for unit testing ViewModels. I'm interested in writing a custom Extesnsion, but I don't really know where to start. Any ideas? Does this already exist?

[autonomousapps]

Actually, turns out it wasn't so hard to replace that particular rule. Here it is:

class InstantTaskExecutorExtension : BeforeEachCallback, AfterEachCallback {

    override fun beforeEach(context: ExtensionContext) {
        ArchTaskExecutor.getInstance().setDelegate(object : TaskExecutor() {
            override fun executeOnDiskIO(runnable: Runnable) {
                runnable.run()
            }

            override fun postToMainThread(runnable: Runnable) {
                runnable.run()
            }

            override fun isMainThread(): Boolean {
                return true
            }
        })
    }

    override fun afterEach(context: ExtensionContext?) {
        ArchTaskExecutor.getInstance().setDelegate(null)
    }
}

[mannodermaus]

Great to see you dived into the Extension sphere yourself already! With the instrumentation test support, I intend to provide replacements for core JUnit 4 APIs that evolve to become Extensions. Since this particular class is tied to Architecture Components, I won't include it into the core instrumentation-test library. However, this could become its own library for people to plug into their project eventually. For now, I'll consider to link to this for the upcoming wiki on usage with Instrumentation Tests. Thank you!

[autonomousapps]

I can confirm that extension works perfectly in my unit test suite. I'll keep an eye on this project and contribute any other extensions I come across (actually, I already have one to enable the @Mock annotation, but I found that elsewhere). I'm sure some way or other we'll end up with some test libs to share!