Write a race condition test for ClientOrders code

[andrzejkrzywda]

Following this post should be fine:
https://blog.arkency.com/2015/09/testing-race-conditions/

The idea is to "justify" the existence of the advisory_lock mechanism. We want to prevent someone removing it by accident/refucktoring and have a failing test for it.
It doesn't need to be mutation testable - it might be expensive.
Some sort of mutant ignore should be fine.
Newest mutant has a way to filter out such calls like advisory_lock.

[andrzejkrzywda]

https://blog.arkency.com/2016/06/cover-all-test-cases-with-permutation/
this may help too