Added test for active channel tracking

To assert that creation and acquisition of a channel from channel pool
do not result in `ActiveChannelTracker` counting it twice.

Author: lutovich

driver/src/test/java/org/neo4j/driver/internal/async/pool/NettyChannelPoolTest.java

@@ -143,7 +143,7 @@ public void shouldAllowAcquireAfterFailures() throws Exception
         {
             try
             {
-                pool.acquire().get( 5, TimeUnit.SECONDS );
+                acquire( pool );
                 fail( "Exception expected" );
             }
             catch ( ExecutionException e )
@@ -154,8 +154,7 @@ public void shouldAllowAcquireAfterFailures() throws Exception
 
         authTokenMap.put( "credentials", value( Neo4jRunner.PASSWORD ) );
 
-        Channel channel = pool.acquire().get( 5, TimeUnit.SECONDS );
-        assertNotNull( channel );
+        assertNotNull( acquire( pool ) );
     }
 
     @Test
@@ -166,13 +165,12 @@ public void shouldLimitNumberOfConcurrentConnections() throws Exception
 
         for ( int i = 0; i < maxConnections; i++ )
         {
-            Channel channel = pool.acquire().get( 5, TimeUnit.SECONDS );
-            assertNotNull( channel );
+            assertNotNull( acquire( pool ) );
         }
 
         try
         {
-            pool.acquire().get( 5, TimeUnit.SECONDS );
+            acquire( pool );
             fail( "Exception expected" );
         }
         catch ( ExecutionException e )
@@ -182,6 +180,29 @@ public void shouldLimitNumberOfConcurrentConnections() throws Exception
         }
     }
 
+    @Test
+    public void shouldTrackActiveChannels() throws Exception
+    {
+        ActiveChannelTracker activeChannelTracker = new ActiveChannelTracker( DEV_NULL_LOGGING );
+
+        poolHandler = activeChannelTracker;
+        pool = newPool( neo4j.authToken() );
+
+        Channel channel1 = acquire( pool );
+        Channel channel2 = acquire( pool );
+        Channel channel3 = acquire( pool );
+        assertEquals( 3, activeChannelTracker.activeChannelCount( neo4j.address() ) );
+
+        release( channel1 );
+        release( channel2 );
+        release( channel3 );
+        assertEquals( 0, activeChannelTracker.activeChannelCount( neo4j.address() ) );
+
+        assertNotNull( acquire( pool ) );
+        assertNotNull( acquire( pool ) );
+        assertEquals( 2, activeChannelTracker.activeChannelCount( neo4j.address() ) );
+    }
+
     private NettyChannelPool newPool( AuthToken authToken )
     {
         return newPool( authToken, 100 );
@@ -195,4 +216,14 @@ private NettyChannelPool newPool( AuthToken authToken, int maxConnections )
         return new NettyChannelPool( neo4j.address(), connector, bootstrap, poolHandler, ChannelHealthChecker.ACTIVE,
                 1_000, maxConnections );
     }
+
+    private static Channel acquire( NettyChannelPool pool ) throws Exception
+    {
+        return pool.acquire().get( 5, TimeUnit.SECONDS );
+    }
+
+    private void release( Channel channel ) throws Exception
+    {
+        pool.release( channel ).get( 5, TimeUnit.SECONDS );
+    }
 }