add container manager test

- add ContainerManagerState test group
- containerCounts should change based on the number of pages

test/lib/unit/container_manager_test.dart

@@ -153,6 +153,34 @@ void main() {
         },
       );
 
+//      testWidgets(
+//        'through the `BoostContainerManager.of(context)` method',
+//        (WidgetTester tester) async {
+//          var builderContext;
+//
+//          await tester.pumpWidget(
+//            MaterialApp(
+//              home: Builder(
+//                builder: (context) {
+//                  return FloatingActionButton(
+//                    onPressed: () {
+//                      builderContext = context;
+//                    },
+//                  );
+//                },
+//              ),
+//            ),
+//          );
+//
+//          expect(find.byType(FloatingActionButton), findsOneWidget);
+//
+//          //get the context of the Builder
+//          await tester.tap(find.byType(FloatingActionButton));
+//
+//          expect(BoostContainerManager.of(builderContext), isAssertionError);
+//        },
+//      );
+
       testWidgets(
         'through the `BoostContainerManager.tryOf(context)` method',
         (WidgetTester tester) async {
@@ -197,4 +225,71 @@ void main() {
       );
     },
   );
+
+  group('ContainerManagerState', () {
+    testWidgets(
+      'containerCounts should change based on the number of pages',
+      (WidgetTester tester) async {
+        var builderContext;
+
+        FlutterBoost.singleton.registerPageBuilders({
+          'context': (pageName, params, _) => Builder(
+                builder: (context) {
+                  return FloatingActionButton(
+                    onPressed: () {
+                      builderContext = context;
+                    },
+                  );
+                },
+              ),
+        });
+
+        await tester.pumpWidget(
+          MaterialApp(
+            builder: FlutterBoost.init(),
+            home: Container(),
+          ),
+        );
+
+        //open first context page
+        ContainerCoordinator.singleton
+            .nativeContainerDidShow("context", {}, "1000000");
+
+        await tester.pump(Duration(seconds: 1));
+
+        //get the context of the Builder
+        await tester.tap(find.byType(FloatingActionButton));
+
+        final containerManagerState = BoostContainerManager.of(builderContext);
+
+        expect(containerManagerState.containerCounts, 1,
+            reason: '1 page shown');
+
+        //open second context page
+        ContainerCoordinator.singleton
+            .nativeContainerDidShow("context", {}, "2000000");
+
+        await tester.pump(Duration(seconds: 1));
+
+        expect(containerManagerState.containerCounts, 2,
+            reason: '2 page shown');
+
+        //pop second context page
+        containerManagerState.pop();
+
+        await tester.pump(Duration(seconds: 1));
+
+        expect(containerManagerState.containerCounts, 1,
+            reason: 'second context page closed, Only one page left');
+
+        //pop last context page
+        containerManagerState.pop();
+
+        await tester.pump(Duration(seconds: 1));
+
+        expect(containerManagerState.containerCounts, 0,
+            reason: 'last context page closed, no page left');
+      },
+    );
+  });
 }