I compare XML documents with XMLUnit Java library. The documentation of XMLUnit is here: https://github.com/xmlunit/user-guide/wiki .
I make a comparisson test case in SoapUI containing steps:
1. Soap request to a service A
2. Soap request to a service B
3. Groovy script to compare the response of step1 with the response of step2
The test case is successfull when all 3 test steps succeed.
I found effective to develop a Java library and place the jar file into bin/ext folder of SoapUI. Then I import my classes in the Groovy script and keep the Groovy code rather small. But you can put XMLUnit jar into your bin/ext folder and start straight away within Groovy script.
Actually, it would be great if SoapUI introduced such functionality out-of-the-box (compare test step), selecting two documents, choosing which way to compare (e.g. structure only) and which parts to ignore (using XPath expressions).
Karel
