in maven-plugin-testing-harness/src/main/java/org/apache/maven/api/plugin/testing/MojoExtension.java [293:305]
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"))
.orElseThrow(
() -> new ConfigurationException("Cannot find a configuration element for a plugin with an "
+ "artifactId of " + artifactId + "."));
return pluginConfigurationElement.getDom();
}