Wait for function to execute?

[Nikolay Kudryavtsev]

Hello.

I have a case where I'm writing a unit test(A) that needs to wait for a 
function(B) that's called by a process sentinel for a process started by 
this unit test. So, when A runs, B runs too, eventually... Since it's a 
unit test, changing B is off limits.

So far I'm thinking of advising B using advice-once described by Drew 
here <https://emacs.stackexchange.com/a/26260/9143>. As my advice 
function I would use a closure that wraps over some condition. Then I 
would have a while loop that sleeps until that condition is fulfilled. 
All this wrapped into one beautiful(ha!) macro. Are there any more, ugh, 
reasonable options?

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Best Regards,
Nikolay Kudryavtsev