@JanPot, the properties of SoapUI objects are not always simple strings.
Sometimes the naming of user interface label does not correspond directly to the object bellow.
In your case the rawRequest triggers the request evaluation (inline groovy code is evaluated) and then you get a brand new raw request. However, it is not the last message exchange of the test step run.
thank you very much for your help. I tried to apply your last solution, but I can't kind a get to understand it... Would you be so helpful and tell me how I could use testRunner.getResults() collection in the context of my example ?