Not sure how to "force" it. What I did in a test is that I try to serialize both the bean and its creational context https://github.com/weld/core/commit/41d85329788772bb871bf981c36a9538cc96daed#diff-5
Ok great that is good to know. Your test is much more eleguant that mine as I used the client side approach and I was therefore not able to catch the exception.
Regarding forcing passivation, the other solution that I found was to limit the number of simultaneous sessions to 1 and to perform 2 requests with two different clients.
Many thanks again for your help