Making Test(Coroutine)Scope sealed breaks my entire test suite

[fluidsonic]

I have the following "scope" interface for all my integration tests (and similar in other kinds of tests):

interface IntegrationTestScope : TestCoroutineScope {
	val client: IntegrationTestClient
	val server: IntegrationTestServer
}

class IntegrationTestScopeImpl(
	override val client: IntegrationTestClient,
	coroutineScope: TestCoroutineScope,
	override val server: IntegrationTestServer,
) : IntegrationTestScope, TestCoroutineScope by coroutineScope

That is to keep TestCoroutineScope functionality in scope while also adding custom functionality.

In 1.6.0-RC that doesn't compile anymore.

Inheritance of sealed classes or interfaces from different module is prohibited

Same with the new TestScope.
What's the reason to make the old one suddenly sealed?
That's a source-breaking change. And it's not listed as a breaking change in the release notes.

The code of TestCoroutineScope has this @Deprecated comment:

Since 1.6.0, ERROR in 1.7.0 and removed as experimental in 1.8.0

Unfortunately it's already an error in 1.6.0 due to sealed.

What's the suggested path forward?

[dkhalanskyjb]

What's the reason to make the old one suddenly sealed?

The reason is that TestScope and TestCoroutineScope have very brittle behavior that could easily be broken by inheriting from them. For example, even before this, doing testScope.runBlockingTest would run the passed block not in the testScope but in a new scope with the same context. This significantly obscures the intent and the behavior of the code.

What's the suggested path forward?

We couldn't think of any use cases for someone inheriting from TestCoroutineScope. However, given that it causes breakage after all, maybe we should un-seal it in the next RC, given how it's deprecated anyway.

As for what can be done on your side, please see the migration guide: https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-test/MIGRATION.md#testcoroutinescope In essence, if you use testScope.runBlockingTest, replace it with runBlockingTest(testScope.coroutineContext). Then, nothing in our API will accept the TestCoroutineScope as an argument, and you can just not implement TestCoroutineScope.

Does this work for you?