考虑以下测试。test shared flow A将通过，但test shared flow B将失败。
我的印象是，这两项声明是相同的。
为什么test shared flow B会失败？
有没有办法让它通过，同时仍然使用launchIn方法？

import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.flow.MutableSharedFlow
import kotlinx.coroutines.flow.flowOn
import kotlinx.coroutines.flow.launchIn
import kotlinx.coroutines.flow.onEach
import kotlinx.coroutines.launch
import kotlinx.coroutines.test.UnconfinedTestDispatcher
import kotlinx.coroutines.test.runTest
import org.junit.Test

@OptIn(ExperimentalCoroutinesApi::class)
class SomethingTest {

    @Test
    fun `test shared flow A`() = runTest {
        val flow = MutableSharedFlow<Int>()
        val items = mutableListOf<Int>()
        val job = launch(UnconfinedTestDispatcher()) {
            flow.collect {
                items.add(it)
            }
        }
        flow.emit(1)
        assert(items.size == 1)
        job.cancel()
    }

    @Test
    fun `test shared flow B`() = runTest {
        val flow = MutableSharedFlow<Int>()
        val items = mutableListOf<Int>()
        val job = flow.onEach { items.add(it) }
            .flowOn(UnconfinedTestDispatcher())
            .launchIn(this)
        flow.emit(1)
        assert(items.size == 1)
        job.cancel()
    }
}