@Before
    public void setup() {
    }
<p>
Test to ensure drain handler fires as expected; when the write queue has been exceeded, and
thus advertises itself as full {@link ISignalWriteStream#isFull}. This enables a simple
back-pressure mechanism which enables the corresponding ingress point to be paused (thus
backing off) until load has decreased.
</p>
<p>
The server then calls {@link HttpServerRequest#resume()}, allowing the queued data to flow
through, simulating a scenario in which the backlog has been cleared. Once the queue has
sufficiently diminished, {@link ISignalWriteStream#drainHandler(IAsyncHandler)} will be
called to indicate that the client can begin sending again.
</p>
<p>
Order of operations:
<ul>
<li>HTTP server initiated which immediately {@link HttpServerRequest#pause()}es any received
requests.</li>
<li>Invoke {@link HttpConnector#write(IApimanBuffer)} on connector until it indicates the
queue {@link HttpConnector#isFull()}.</li>
<li>{@link HttpServerRequest#resume} HTTP server to consume (and thus reduce) incoming
queue.</li>
<li>{@link ISignalWriteStream#drainHandler(IAsyncHandler)} is invoked once queue is
sufficiently small (as determined by impl which at time of writing is maxSize/2).</li>
</ul>

<p>
The drain handler is sometimes called multiple times, I think it's okay though.
</p>

@author Marc Savy {@literal <msavy@redhat.com>}
gateway/platforms/vertx3/vertx3/src/test/java/io/apiman/gateway/platforms/vertx3/connector/HttpConnectorDrainTest.java