This would be a rose by a different name. So long as you're testing your branch's state, and not the end result of the merge — as most CI systems & GitHub end up pushing people towards — you're going to run into problems.

What makes testing the end result of the merge tricky, I suppose, is that it changes over time. (As other people merge into whatever "stabilize branch" you have, the result of merging your branch and the new HEAD of the stabilize branch must change.)