Jest Unit Test on Ionic app

I am trying to test my Ionic app with Jest instead of the traditional Jasmine and Karma. I can run simple test like

expect(1).toEqual(1)

and test passed with no problem.

The issue that I am having is testing services. I have something like

expect(CalculatorService).toBeDefined();

and test will result as passed indicating the service is defined. However when I tried to invoke the method of CalculatorService

expect(CalculatorService.add(1,1).toEqual(2)

results in

"TypeError: CalculatorService.add is not a function"

I know with Jasmine & Karma we need to inject the service. But I don't know what's the equivalent for Jest.

Can someone shed some light?