Fix flakiness in MessagingAnalyticsRoboTest.java (#4259)

Properly reset SharedPreferences test state in between each test.

Author: willxu-google

firebase-messaging/src/test/java/com/google/firebase/messaging/MessagingAnalyticsRoboTest.java

@@ -105,6 +105,9 @@ public void setUp() {
 
     // Create and Initialize Firelog service components
     context = ApplicationProvider.getApplicationContext();
+
+    // Reset sharedpreferences for bigquery delivery metrics export before every test.
+    resetPreferencesField(DELIVERY_METRICS_EXPORT_TO_BIG_QUERY_PREF);
   }
 
   /** If the developer didn't include Analytics and Firelog, we should not crash. */
@@ -331,6 +334,13 @@ public void testShouldExportDeliveryMetricsToBigQuery_falseManifestTrueSetter()
     assertPreferencesFieldWithValue(DELIVERY_METRICS_EXPORT_TO_BIG_QUERY_PREF, true);
   }
 
+  private void resetPreferencesField(String field) {
+    SharedPreferences preferences =
+        context.getSharedPreferences(FCM_PREFERENCES, Context.MODE_PRIVATE);
+
+    preferences.edit().remove(field).apply();
+  }
+
   private void assertPreferencesFieldWithValue(String field, Boolean expectedValue) {
     SharedPreferences preferences =
         context.getSharedPreferences(FCM_PREFERENCES, Context.MODE_PRIVATE);