On the PHP in Action blog, despite some agreement with Padraic Brady on his one behavior, one assertion method for writing unit tests, Dagfinn Reiersol still has his reservations.

Pádraic maintains that one assertion per test is a rule that should always be followed unless there is a specific good reason to break it. I prefer it as a guideline, as does Robert C. Martin in the book Clean Code. The reference is not intended as an appeal to authority to "prove" that I’m right. I’m just making the point that I think this reflects the current state of the art, which is not necessarily perfect, of course.

Dagfinn talks about behavior-driven development and illustrates how a two assertions could be combined into one but that the end result "isn't very pretty" - and that's just testing two proterties of a single object. Imagine what would happen if things got more complex.