Fix bug in unmountWidgetAdId (#42)

Author: Emmanuel Garcia

packages/google_mobile_ads/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 0.11.0+2
 
 * Set min Android version to `19`.
+* Fixes bug that displayed "This AdWidget is already in the Widget tree".
 
 ## 0.11.0+1
 

packages/google_mobile_ads/lib/src/ad_instance_manager.dart

@@ -116,7 +116,7 @@ class AdInstanceManager {
   void mountWidgetAdId(int adId) => _mountedWidgetAdIds.add(adId);
 
   /// Indicates that [adId] is unmounted from the widget tree.
-  void unmountWidgetAdId(int adId) => _mountedWidgetAdIds.add(adId);
+  void unmountWidgetAdId(int adId) => _mountedWidgetAdIds.remove(adId);
 
   /// Starts loading the ad if not previously loaded.
   ///

packages/google_mobile_ads/test/ad_containers_test.dart

@@ -227,6 +227,9 @@ void main() {
         listener: AdListener(),
         request: AdRequest(),
       );
+
+      await ad.load();
+
       try {
         await tester.pumpWidget(
           Directionality(
@@ -265,6 +268,9 @@ void main() {
         listener: AdListener(),
         request: AdRequest(),
       );
+
+      await ad.load();
+
       final AdWidget widget = AdWidget(ad: ad);
       try {
         await tester.pumpWidget(
@@ -306,6 +312,7 @@ void main() {
         listener: AdListener(),
         request: AdRequest(),
       );
+      await ad.load();
       final AdWidget widget = AdWidget(ad: ad);
       try {
         await tester.pumpWidget(
@@ -318,6 +325,9 @@ void main() {
             ),
           ),
         );
+
+        await tester.pumpWidget(Container());
+
         await tester.pumpWidget(
           Directionality(
             textDirection: TextDirection.ltr,