void unregisterSourceReader(int subtaskId, int attemptNumber) {
        final Map<Integer, ReaderInfo> attemptReaders = registeredReaders.get(subtaskId);
        if (attemptReaders != null) {
            attemptReaders.remove(attemptNumber);

            if (attemptReaders.isEmpty()) {
                registeredReaders.remove(subtaskId);
            }
        }
    }
@Test
    void testUnregisterUnregisteredReader() {
        context.unregisterSourceReader(0, 0);
    }