Possibly this is better:

"suspended when in testing mode. This helps ensure that your code and the tests you write for that code will execute in an expected sequence: one that you can depend on when running tests around that code. Note that in testing Promises and asynchronous code, you're effectively "stepping through" your application in chunks, running your test assertion code in appropriate places to ensure that things are as you would expect, and exactly when you expect them to be."

Hopefully that's clearer?