why observer can't fire in rspec? help .

I read the guide and api and i created Observer on model, she can run on rails console of test env. but when i use rspec , the observer can't run in, it's never step in.

some good man help me, please. i debug it use one day and one night, i can't sleep in today night unless i solve it.

Does this help?

very thank you. i know how to test observer now. but i can't understand why observer can't run in spec?