gateway session test added for a weak map with awaitility

common/transport/mqtt/pom.xml

@@ -88,6 +88,11 @@
             <artifactId>junit</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.awaitility</groupId>
+            <artifactId>awaitility</artifactId>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-core</artifactId>

common/transport/mqtt/src/test/java/org/thingsboard/server/transport/mqtt/session/GatewaySessionHandlerTest.java

@@ -0,0 +1,46 @@
+package org.thingsboard.server.transport.mqtt.session;
+
+import org.junit.Test;
+
+import java.util.WeakHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+import static org.awaitility.Awaitility.await;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.BDDMockito.willCallRealMethod;
+import static org.mockito.Mockito.mock;
+
+public class GatewaySessionHandlerTest {
+
+    @Test
+    public void givenWeakHashMap_WhenGC_thenMapIsEmpty() {
+        WeakHashMap<String, Lock> map = new WeakHashMap<>();
+
+        String deviceName = new String("device"); //constants are static and doesn't affected by GC, so use new instead
+        map.put(deviceName, new ReentrantLock());
+        assertTrue(map.containsKey(deviceName));
+
+        deviceName = null;
+        System.gc();
+
+        await().atMost(10, TimeUnit.SECONDS).until(() -> !map.containsKey("device"));
+    }
+
+    @Test
+    public void givenConcurrentReferenceHashMap_WhenGC_thenMapIsEmpty() {
+        GatewaySessionHandler gsh = mock(GatewaySessionHandler.class);
+        willCallRealMethod().given(gsh).createWeakMap();
+
+        ConcurrentMap<String, Lock> map = gsh.createWeakMap();
+        map.put("device", new ReentrantLock());
+        assertTrue(map.containsKey("device"));
+
+        System.gc();
+
+        await().atMost(10, TimeUnit.SECONDS).until(() -> !map.containsKey("device"));
+    }
+
+}