Fix flaky JUnit test

This test sometimes fails in PostSubmits because the background
thread which calls the verified class does not have time to execute
before the class is verified.

This creates a helper function to monitor background thread completion.

Test: atest -c AutoSelectPreferenceControllerTest
Change-Id: I6c320abd70fcb5fe823ec122fb0dac67174ecb4a

tests/unit/src/com/android/settings/network/telephony/gsm/AutoSelectPreferenceControllerTest.java

@@ -18,6 +18,7 @@ package com.android.settings.network.telephony.gsm;
 
 import static com.google.common.truth.Truth.assertThat;
 
+import static org.junit.Assert.fail;
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.verify;
@@ -42,6 +43,9 @@ import org.mockito.Answers;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
+
 @RunWith(AndroidJUnit4.class)
 public class AutoSelectPreferenceControllerTest {
     private static final int SUB_ID = 2;
@@ -93,7 +97,14 @@ public class AutoSelectPreferenceControllerTest {
         when(mTelephonyManager.getNetworkSelectionMode()).thenReturn(
             TelephonyManager.NETWORK_SELECTION_MODE_AUTO);
 
-        assertThat(mController.setChecked(true)).isFalse();
+        // Wait for asynchronous thread to finish, otherwise test will flake.
+        Future thread = mController.setAutomaticSelectionMode();
+        try {
+            thread.get();
+        } catch (ExecutionException | InterruptedException e) {
+            e.printStackTrace();
+            fail("Exception during automatic selection");
+        }
 
         verify(mProgressDialog).show();
         verify(mTelephonyManager).setNetworkSelectionModeAutomatic();
@@ -136,4 +147,4 @@ public class AutoSelectPreferenceControllerTest {
     public String resourceString(String name, Object value) {
         return mContext.getResources().getString(resourceId("string", name), value);
     }
-}
+}