private void verifyNonEmptyImmediatelyConnectedKeys(Selector selector) throws Exception {
        Field field = Selector.class.getDeclaredField("immediatelyConnectedKeys");
        field.setAccessible(true);
        Collection<?> immediatelyConnectedKeys = (Collection<?>) field.get(selector);
        assertFalse(immediatelyConnectedKeys.isEmpty());
    }
Validate that correct subset of io metrics marked deprecated in docs
clients/src/test/java/org/apache/kafka/common/network/SelectorTest.java