I'm getting that exact same issue on Windows : https://community.smartbear.com/t5/SoapUI-Open-Source/quot-Add-Assertion-quot-Window-Not-Allowing-to-Add-Assertions/m-p/158051#M26199. So it looks like it might relate more to your environment than to the fact its Mac or Win.
Interesting solution with the pull and build. You didn't have to change anything?
Hi - I am not sure about your question - I did change one file as you can see in the commits. If yours is the same problem as mine, you can take my fork and compile from there as long as the pull request is not merged in upstream. If you are unsure how to do that, I can provide you with the compiled JAR file. Please send me a mail to carsten.heidmann(at)disy.net if I can help you with that.
