Can you please show your test case structure or a screen shot of it?
Is the above a groovy script step? or script assertion.
From the error message, it appears that you were expectecting 'testRequest' for a Property Test step as well and this is incorrect.
You need to set the request conditionally i.e., if the particular step is instance of SOAP or JDBC or REST or HTTP, then only would be able to set the request.
See if the below example helps for checking the instanceof:
https://github.com/nmrao/soapUIGroovyScripts/blob/ed7398271673b57a89935e1fba98c813b387de56/groovy/UpdateResponseSLA.groovy
