Add a test to identify memory leak in ConnectivityManager

The sInstance static instance which self reference to
ConnectivityManager which holds a reference to a ConnectivityManager
instance causes the Context referenced by that instance to never be
GCed.

Bug: 202978965
Test: atest ConnectivityManagerTest
Change-Id: I0227f63dbc27688ea5f4ef9275fd0f9c247ad14c

tests/unit/java/android/net/ConnectivityManagerTest.java

@@ -72,6 +72,7 @@ import android.os.Process;
 
 import androidx.test.filters.SmallTest;
 
+import com.android.internal.util.test.BroadcastInterceptingContext;
 import com.android.testutils.DevSdkIgnoreRule;
 import com.android.testutils.DevSdkIgnoreRunner;
 
@@ -82,6 +83,8 @@ import org.mockito.ArgumentCaptor;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
+import java.lang.ref.WeakReference;
+
 @RunWith(DevSdkIgnoreRunner.class)
 @SmallTest
 @DevSdkIgnoreRule.IgnoreUpTo(VERSION_CODES.R)
@@ -461,4 +464,50 @@ public class ConnectivityManagerTest {
         }
         fail("expected exception of type " + throwableType);
     }
+
+    private static class MockContext extends BroadcastInterceptingContext {
+        MockContext(Context base) {
+            super(base);
+        }
+
+        @Override
+        public Context getApplicationContext() {
+            return mock(Context.class);
+        }
+    }
+
+    private WeakReference<Context> makeConnectivityManagerAndReturnContext() {
+        // Mockito may have an internal reference to the mock, creating MockContext for testing.
+        final Context c = new MockContext(mock(Context.class));
+
+        new ConnectivityManager(c, mService);
+
+        return new WeakReference<>(c);
+    }
+
+    private void forceGC() {
+        // First GC ensures that objects are collected for finalization, then second GC ensures
+        // they're garbage-collected after being finalized.
+        System.gc();
+        System.runFinalization();
+        System.gc();
+    }
+
+    @Test
+    public void testConnectivityManagerDoesNotLeakContext() throws Exception {
+        final WeakReference<Context> ref = makeConnectivityManagerAndReturnContext();
+
+        final int attempts = 100;
+        final long waitIntervalMs = 50;
+        for (int i = 0; i < attempts; i++) {
+            forceGC();
+            if (ref.get() == null) break;
+
+            Thread.sleep(waitIntervalMs);
+        }
+
+        // TODO: fix memory leak then assertNull here.
+        assertNotNull("Couldn't find the Context leak in ConnectivityManager after " + attempts
+                + " attempts", ref.get());
+    }
 }