Fix deadlock in espresso in Robolectric INSTRUMENTATION_TEST + paused looper.

When running tests in Robolectric's INSTRUMENTATION_TEST LooperMode
and explicitly pausing the main looper, Espresso will deadlock if part of its
AsyncTask initialization occurs on the test thread.

Fix this by adding a call to explict call to ControlledLooper.drainMainThreadWhenIdle.

PiperOrigin-RevId: 704231969

Author: brettchabot

espresso/CHANGELOG.md

@@ -16,6 +16,8 @@ The following artifacts were released:
 
 **Bug Fixes**
 
+* Fix deadlock in espresso in Robolectric INSTRUMENTATION_TEST + paused looper.
+
 **New Features**
 
 **Breaking Changes**

espresso/core/java/androidx/test/espresso/base/ThreadPoolExecutorExtractor.java

@@ -19,6 +19,8 @@
 import android.os.Handler;
 import android.os.Looper;
 import androidx.annotation.Nullable;
+import androidx.test.internal.platform.ServiceLoaderWrapper;
+import androidx.test.internal.platform.os.ControlledLooper;
 import java.lang.reflect.Field;
 import java.util.concurrent.Callable;
 import java.util.concurrent.CountDownLatch;
@@ -42,6 +44,10 @@ final class ThreadPoolExecutorExtractor {
   private static final String MODERN_ASYNC_TASK_FIELD_NAME = "THREAD_POOL_EXECUTOR";
   private final Handler mainHandler;
 
+  private final ControlledLooper controlledLooper =
+      ServiceLoaderWrapper.loadSingleService(
+          ControlledLooper.class, () -> ControlledLooper.NO_OP_CONTROLLED_LOOPER);
+
   @Inject
   ThreadPoolExecutorExtractor(Looper looper) {
     mainHandler = new Handler(looper);
@@ -85,6 +91,7 @@ public void run() {
             }
           });
       try {
+        controlledLooper.drainMainThreadUntilIdle();
         latch.await();
       } catch (InterruptedException ie) {
         if (!futureToRun.isDone()) {