Github user pnowojski commented on a diff in the pull request: https://github.com/apache/flink/pull/4533#discussion_r145980535 --- Diff: flink-runtime/src/test/java/org/apache/flink/runtime/io/network/netty/PartitionRequestClientHandlerTest.java --- @@ -208,6 +211,53 @@ public void testCancelBeforeActive() throws Exception { client.cancelRequestFor(inputChannel.getInputChannelId()); } + /** + * Verifies that {@link RemoteInputChannel} is enqueued in the pipeline, and + * {@link AddCredit} message is sent to the producer. + */ + @Test + public void testNotifyCreditAvailable() throws Exception { + final CreditBasedClientHandler handler = new CreditBasedClientHandler(); + final EmbeddedChannel channel = new EmbeddedChannel(handler); + + final RemoteInputChannel inputChannel = mock(RemoteInputChannel.class); --- End diff -- I know that mocking was extensively used so far, but we had quite bad experience with it. I don't agree that it is not interacting, because it is for example checking `inputChannel.isReleased()`, which you need to mock one test below. Now imagine that during some refactor/implementing new feature someone modifies handlers code, by adding some additional interaction/sanity check on `inputChannel`. With mocks it will lead with thousands of changes in all of the mocked unit tests.
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