为什么在操场和单元测试中不调用GCD调度组notify

I have the code working in simulator/device and I'm trying to write unit tests for it. However, notify callback is not called in unit tests. Here's is a code for Playgrounds which is also not calling notify callback. I suspect it I may be using the wrong queue, but cannot figure out which one I should use.I have the code working in simulator/device and