Idea how to find bugs or bad behaviour of multi-pv

[Uri Blass]

Of course I do not expect engines to play at the same strength when they need to give score for more than 1 move but I expect 2 things from engines without bugs.
1)I expect multi-pv not to be weaker than one option at fixed depth.
2)I expect multi-pv with n options that get n:1 time advantage not to be weaker relative to one option.

I wonder if somebody tested if engines with multi-pv obey to these rules. Of course obeying to these rules does not mean that there are no bugs in the quality of the second best move or the third best move and I guess we need a different test to test it.