Using scripting to choose a response based on the request

You can just use Xpath for dispatch. The result of the Xpath query is the name of the MockResponse that SoapUI will use. So if the MockResponse is exactly the same as the id you want to test for then, then just hit the declare button and then:

//*:id

A dispatch script works the same way, just have it return the name of the MockResponse you want to give:

import groovy.util.XmlSlurper
import groovy.util.slurpersupport.GPathResult
GPathResult Envelope = new XmlSlurper().parseText(mockRequest.requestContent)
return Envelope.Body.Id

Which you can write as a one-liner if you want:

new groovy.util.XmlSlurper().parseText(mockRequest.requestContent).Body.Id