in maven-plugin-testing-harness/src/main/java/org/apache/maven/api/plugin/testing/MojoExtension.java [578:588]
public static XmlNode extractPluginConfiguration(String artifactId, Xpp3Dom pomDom) throws Exception {
Xpp3Dom pluginConfigurationElement = child(pomDom, "build")
.flatMap(buildElement -> child(buildElement, "plugins"))
.map(MojoExtension::children)
.orElseGet(Stream::empty)
.filter(e -> e.getChild("artifactId").getValue().equals(artifactId))
.findFirst()
.flatMap(buildElement -> child(buildElement, "configuration"))
.orElse(Xpp3DomBuilder.build(new StringReader("<configuration/>")));
return pluginConfigurationElement.getDom();
}