超时测试-java.lang.RuntimeException：找不到活动

Question

Android Studio 3.3，Koltlin 1.3 Java 1.8

这是我的Espresso对MockWebServer的测试。

import androidx.test.espresso.matcher.ViewMatchers.*
import androidx.test.runner.AndroidJUnit4  
import java.util.concurrent.TimeUnit

@RunWith(AndroidJUnit4::class)
class AddTraderActivityNetworkTest {
    private lateinit var mockServer: MockWebServer

    @Rule
    @JvmField
    var addTraderIntentTestRule: IntentsTestRule<AddTraderActivity> = IntentsTestRule(AddTraderActivity::class.java)

    @Before
    fun setup() {
        mockServer = MockWebServer()
        mockServer.start(8081)
     }

    @Test
    fun buttonStart_click_serverError_showToast() {
        mockServer.enqueue(MockResponse()
                .setResponseCode(500))

        onView(withId(R.id.startButton))
                .perform(click())
        onView(withText(R.string.server_error)).inRoot(ToastMatcher())
                .check(matches(isDisplayed()))
    }

     @Test
    fun buttonStart_click_timeOut_showToast() {
        mockServer.enqueue(MockResponse()
                .setResponseCode(200)
                .throttleBody(1024, 1, TimeUnit.SECONDS)) 

        onView(withId(R.id.startButton))
                .perform(click())
        onView(withText(R.string.service_unavailable)).inRoot(ToastMatcher())
                .check(matches(isDisplayed()))
    }

    @After
    @Throws
    fun tearDown() {
        // We're done with tests, shut it down
        mockServer.shutdown()
    }
}

开始测试buttonStart_click_serverError_showToast时，测试成功。但是当我开始测试buttonStart_click_timeOut_showToast时，我得到了错误：

java.lang.RuntimeException: No activities found. Did you forget to launch the activity by calling getActivity() or startActivitySync or similar?
at androidx.test.espresso.base.RootViewPicker.waitForAtLeastOneActivityToBeResumed(RootViewPicker.java:169)

我该如何解决？ 我开始活动，但出现错误。为什么？