Fix ByteBuf leak in Http2ControlFrameLimitEncoderTest (netty#9466)

Motivation:

We recently introduced Http2ControlFrameLimitEncoderTest which did not correctly notify the goAway promises and so leaked buffers.

Modifications:

Correctly notify all promises and so release the debug data.

Result:

Fixes leak in HTTP2 test

codec-http2/src/test/java/io/netty/handler/codec/http2/Http2ControlFrameLimitEncoderTest.java

@@ -38,6 +38,9 @@
 import org.mockito.stubbing.Answer;
 
 
+import java.util.ArrayDeque;
+import java.util.Queue;
+
 import static io.netty.handler.codec.http2.Http2CodecUtil.*;
 import static io.netty.handler.codec.http2.Http2Error.CANCEL;
 import static io.netty.handler.codec.http2.Http2Error.ENHANCE_YOUR_CALM;
@@ -71,6 +74,8 @@ public class Http2ControlFrameLimitEncoderTest {
 
     private int numWrites;
 
+    private Queue<ChannelPromise> goAwayPromises = new ArrayDeque<ChannelPromise>();
+
     /**
      * Init fields and do mocking.
      */
@@ -116,7 +121,9 @@ public ChannelFuture answer(InvocationOnMock invocationOnMock) {
             @Override
             public ChannelFuture answer(InvocationOnMock invocationOnMock) {
                 ReferenceCountUtil.release(invocationOnMock.getArgument(3));
-                return handlePromise(invocationOnMock, 4);
+                ChannelPromise promise = invocationOnMock.getArgument(4);
+                goAwayPromises.offer(promise);
+                return promise;
             }
         });
         Http2Connection connection = new DefaultHttp2Connection(false);
@@ -168,6 +175,16 @@ private ChannelPromise handlePromise(InvocationOnMock invocationOnMock, int prom
     public void teardown() {
         // Close and release any buffered frames.
         encoder.close();
+
+        // Notify all goAway ChannelPromise instances now as these will also release the retained ByteBuf for the
+        // debugData.
+        for (;;) {
+            ChannelPromise promise = goAwayPromises.poll();
+            if (promise == null) {
+                break;
+            }
+            promise.setSuccess();
+        }
     }
 
     @Test
@@ -254,12 +271,6 @@ private void verifyFlushAndClose(int invocations, boolean failed) {
         }
     }
 
-    private static void assertWriteFailure(ChannelFuture future) {
-        Http2Exception exception = (Http2Exception) future.cause();
-        assertEquals(ShutdownHint.HARD_SHUTDOWN, exception.shutdownHint());
-        assertEquals(Http2Error.ENHANCE_YOUR_CALM, exception.error());
-    }
-
     private ChannelPromise newPromise() {
         return new DefaultChannelPromise(channel, ImmediateEventExecutor.INSTANCE);
     }