private Node createNode(String applicationName, ServiceType serviceType) {
        Application application = new Application(applicationName, serviceType);
        return new Node(application);
    }
Checks histograms for user node.
<pre>
    userNode ---> wasNode (2 agents)
</pre>
web/src/test/java/com/navercorp/pinpoint/web/applicationmap/appender/histogram/NodeHistogramAppenderTest.java