It will be sort of a pain, but here is what you can do:
1) Figure out an Xpath 'base' using the assertion tab (sounds like you are here already). I used this public site to test against: http://graphical.weather.gov/xml/DWMLgen/wsdl/ndfdXML.wsdl
I used the CornerPoints method with 'hawaii' as the single param.
I created this 'base' xpath:
declare namespace ns1='http://graphical.weather.gov/xml/DWMLgen/wsdl/ndfdXML.wsdl';
declare namespace SOAP-ENC='http://schemas.xmlsoap.org/soap/encoding/';
declare namespace SOAP-ENV='http://schemas.xmlsoap.org/soap/envelope/';
/SOAP-ENV:Envelope/SOAP-ENV:Body/ns1:CornerPointsResponse/listLatLonOut
(it will write the declare statements for you if you click declare)
(which you can test out in the assertions window)
2) Create a Properties step
3) Create a Property transfer step
4) Create a groovy script
5) add a property... i called mine misc
6) add a transfer step
* transfer from the CornerPoints - Request 1 --- Response
* paste the Xpath stuff in the box under the 'transfer from'
* Transfer to your property
(You can test with the little play button)
7) Add something like this to your groovy script:
def x = context.expand( '${Properties#misc}' )
def parts = x.tokenize(',')
for (def part in parts)
{
log.info(part)
if (part.startsWith("-153"))
log.info("good")
}
In the groovy step you can do anything you need to get at your (partial) data. The sample code I added gets lat/lons out of a long line wrapped in CDATA and then checks for just the starting part of some of the data.. just an example.
Remember that you can use groovy and java string methods:
http://groovy.codehaus.org/groovy-jdk/java/lang/String.html
http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/String.html
More groovy tips:
http://www.soapui.org/Scripting-Properties/tips-a-tricks.html