@Test
    public void testCallDisconnect() {
        awaitReady(client, node);
        assertTrue(client.isReady(node, time.milliseconds()),
            "Expected NetworkClient to be ready to send to node " + node.idString());
        assertFalse(client.connectionFailed(node),
            "Did not expect connection to node " + node.idString() + " to be failed");
        client.disconnect(node.idString());
        assertFalse(client.isReady(node, time.milliseconds()),
            "Expected node " + node.idString() + " to be disconnected.");
        assertTrue(client.connectionFailed(node),
            "Expected connection to node " + node.idString() + " to be failed after disconnect");
        assertFalse(client.canConnect(node, time.milliseconds()));

        // ensure disconnect does not reset backoff period if already disconnected
        time.sleep(reconnectBackoffMaxMsTest);
        assertTrue(client.canConnect(node, time.milliseconds()));
        client.disconnect(node.idString());
        assertTrue(client.canConnect(node, time.milliseconds()));
    }
This is a helper method that will execute two produce calls. The first call is expected to work and the
second produce call is intentionally made to emulate a request timeout. In the case that a timeout occurs
during a request, we want to ensure that we {@link Metadata#requestUpdate() request a metadata update} so that
on a subsequent invocation of {@link NetworkClient#poll(long, long) poll}, the metadata request will be sent.

<p/>

The {@link MetadataUpdater} has a specific method to handle
{@link NetworkClient.DefaultMetadataUpdater#handleServerDisconnect(long, String, Optional) server disconnects}
which is where we {@link Metadata#requestUpdate() request a metadata update}. This test helper method ensures
that is invoked by checking {@link Metadata#updateRequested()} after the simulated timeout.

@param requestTimeoutMs Timeout in ms
clients/src/test/java/org/apache/kafka/clients/NetworkClientTest.java