我将以如下方式创建ViewAction：

public static ViewAction doTaskInUIThread(final Runnable r) {
    return new ViewAction() {
        @Override
        public Matcher<View> getConstraints() {
            return isRoot();
        }

        @Override
        public String getDescription() {
            return null;
        }

        @Override
        public void perform(UiController uiController, View view) {
            r.run();
        }
    };
}

然后使用下面的命令启动应该在UI线程中运行的代码

onView(isRoot()).perform(doTaskInUIThread(new Runnable() {
        @Override
        public void run() {
            //Code to add your fragment or anytask that you want to do from UI Thread
        }
    }));

以下是添加片段视图层次结构的测试用例示例

@Test
public void testSelectionOfTagsAndOpenOtherPage() throws Exception{

    Runnable r = new Runnable() {
        @Override
        public void run() {
            //Task that need to be done in UI Thread (below I am adding a fragment)

        }
    };
    onView(isRoot()).perform(doTaskInUIThread(r));

}

public class VoiceFullScreenTest {
    @Rule
    public ActivityTestRule activityRule = new ActivityTestRule<>(
            TestActivity.class);

    @Test
    public void fragment_can_be_instantiated() {
        activityRule.getActivity().runOnUiThread(new Runnable() {
            @Override
            public void run() {
                VoiceFragment voiceFragment = startVoiceFragment();
            }
        });
        // Then use Espresso to test the Fragment
        onView(withId(R.id.iv_record_image)).check(matches(isDisplayed()));
    }

    private VoiceFragment startVoiceFragment() {
        TestActivity activity = (TestActivity) activityRule.getActivity();
        FragmentTransaction transaction = activity.getSupportFragmentManager().beginTransaction();
        VoiceFragment voiceFragment = new VoiceFragment();
        transaction.add(voiceFragment, "voiceFragment");
        transaction.commit();
        return voiceFragment;
    }

}

您可以从UI线程启动您的片段，如上所述。

您可以使用androidx.fragment:fragment-testing库。在测试方法中启动片段非常简单：

val fragmentArgs = Bundle()
androidx.fragment.app.testing.launchFragmentInContainer<MyFragment>(fragmentArgs)

您可以在Test your fragments Android开发者指南中找到有关此库的更多信息。

您可以使用FragmentTestRule。
而不是常规的ActivityTestRule，你必须用途：

@Rule
public FragmentTestRule<?, FragmentWithoutActivityDependency> fragmentTestRule =
    FragmentTestRule.create(FragmentWithoutActivityDependency.class);

你可以找到more details in this blog post。

你可能忘了在视图层次结构中注入片段。尝试在TestActivity布局中定义片段的保持器容器（比如id为fragment_container的FrameLayout），然后使用add(R.id.fragment_container, myFragment, "tag")（this method）代替add(myFragment, "tag")。我猜你也可以使用具有相同签名的replace方法。