class ClassUnderTest(private val mainScope: CoroutineScope, private val bgDispatcher: CoroutineDispatcher {
    fun doSomething() {
        mainScope.launch {
            val data = withContext(bgDispatcher) {
                delay(1000)
                42
            }
            doSomethingWithData(data)
        }
    }
}

private val testBgDispatcher = TestCoroutineDispatcher()
private val testScope = TestCoroutineScope()
private lateinit var subject: ClassUnderTest

@BeforeEach
fun setUp() {
    subject = ClassUnderTest(testScope, testBgDispatcher)
}

@Test
fun testSomething() {
    subject.doSomething()
    testScope.advanceUntilIdle()
}

private val testBgDispatcher = TestCoroutineDispatcher()
private val testScope = TestCoroutineScope(testBgDispatcher)

subject = ClassUnderTest(testScope, testScope.dispatcher)