title: Method getMainLooper in android.os.Looper not mocked still occuring even after adding RxImmediateSchedulerRule
body: <p>TrendingViewModelTest </p>
  
  <pre><code>@RunWith(JUnit4::class)
  class TrendingViewModelTest {
      private lateinit var trendingRepository: TrendingRepository
      private lateinit var trendingViewModel: TrendingViewModel
  
      @get:Rule
      val schedulers = RxImmediateSchedulerRule()
  
      @Before
      fun setUp() {
          trendingRepository = mock(TrendingRepository::class.java)
          trendingViewModel = TrendingViewModel(trendingRepository)
      }
  
      @Test
      fun testWithNetwork() {
          trendingViewModel.isConnected = true
          trendingViewModel.fetchTrendingRepos()
          verify(trendingRepository, times(1)).getTrendingRepos()
      }
  
      //...
  }
  </code></pre>
  
  <p>TrendingViewModel</p>
  
  <pre><code>fun fetchTrendingRepos() {
  if (isConnected) {
      loadingProgress.value = true
      compositeDisposable.add(
          trendingRepository.getTrendingRepos().subscribeOn(Schedulers.io())
              .observeOn(AndroidSchedulers.mainThread())
              .subscribe({ response -&gt;
                  run {
                      loadingProgress.value = false
              },
                  { error -&gt;
                      loadingProgress.value = false
                  }
              )
      )
  } 
  </code></pre>
  
  <p>RxImmediateSchedulerRule:</p>
  
  <pre><code>class RxImmediateSchedulerRule : TestRule {
      override fun apply(base: Statement?, description: Description?): Statement {
          return object : Statement() {
              @Throws(Throwable::class)
              override fun evaluate() {
                  RxJavaPlugins.setIoSchedulerHandler { Schedulers.trampoline() }
                  RxJavaPlugins.setComputationSchedulerHandler { Schedulers.trampoline() }
                  RxJavaPlugins.setNewThreadSchedulerHandler { Schedulers.trampoline() }
                  RxAndroidPlugins.setInitMainThreadSchedulerHandler { Schedulers.trampoline() }
  
                  try {
                      base?.evaluate()
                  } finally {
                      RxJavaPlugins.reset()
                      RxAndroidPlugins.reset()
                  }
              }
          }
      }
  }
  </code></pre>
  
  <p>TrendingRepositoryImpl:</p>
  
  <pre><code>class TrendingRepositoryImpl @Inject constructor(
      val apiService: GitHubApi,
      val trendingDao: AppDao
  ) : TrendingRepository {
  
      override fun getTrendingRepos(): Single&lt;List&lt;TrendingRepo&gt;&gt; {
          return apiService.getTrendingGits()
      }
  }
  </code></pre>
  
  <p>TrendingRepository:</p>
  
  <pre><code>interface TrendingRepository {
      fun getTrendingRepos(): Single&lt;List&lt;TrendingRepo&gt;&gt;
  }
  </code></pre>
  
  <p>Inside <code>fetchTrendingRepos()</code> an Rxjava call is initiated, it also hooks onto 'AndroidSchedulers.mainThread()' that might be the reason causing it.</p>
  
  <blockquote>
    <p>java.lang.RuntimeException: Method getMainLooper in android.os.Looper not mocked.
    at android.os.Looper.getMainLooper(Looper.java)
        at androidx.arch.core.executor.DefaultTaskExecutor.isMainThread(DefaultTaskExecutor.java:77)
        at androidx.arch.core.executor.ArchTaskExecutor.isMainThread(ArchTaskExecutor.java:116)
        at androidx.lifecycle.LiveData.assertMainThread(LiveData.java:461)
        at androidx.lifecycle.LiveData.setValue(LiveData.java:304)
        at androidx.lifecycle.MutableLiveData.setValue(MutableLiveData.java:50)
        at com.manoj.trendgitz.mvvm.ui.TrendingViewModel.fetchTrendingRepos(TrendingViewModel.kt:32)
        at com.manoj.trendgitz.TrendingViewModelTest.testWithNetwork(TrendingViewModelTest.kt:52)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
        at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
        at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
        at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
        at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
        at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
        at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
        at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
        at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
        at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
        at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
        at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
        at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
        at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
        at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
        at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)</p>
  </blockquote>