How to mock generator functions in jest and redux-saga-test-plan?

Question

I am new to redux-saga testing.

I am trying to write tests for the following generator functions, using jest and redux-saga-test-plan:

//saga.ts
export function* chooseCorrectGenerator(action: {type: string, payload: { flag: boolean } }){
   if(action.payload.flag) {
       yield* behaviour1(action);
   }
   else {
       yield* behaviour2(action);
   }
}

export function* behaviour1(action: { type: string, payload: { flag: boolean } }) {
// do work
}

export function* behaviour2(action: { type: string, payload: { flag: boolean } }) {
// do work
}

I want to write a test that checks if the flag is set to true, the behaviour1 function is called. I have separate tests for behaviour1, so I wish to mock its implementation.

This:

// saga.test.ts
import * as sagaFunctions from './saga';
import { expectSaga } from 'redux-saga-test-plan';

test('behaviour test', async () => {
    const testSpy = jest.spyOn(sagaFunctions, "behaviour1");
    await expectSaga(sagaFunctions.chooseCorrectGenerator, {
        type: "TEST_ACTION",
        payload: { flag: true}
    })
    .run();
    expect(testSpy).toBeCalled();
});

Results in:

    expect(jest.fn()).toBeCalled()

    Expected number of calls: >= 1
    Received number of calls:    0

Please note this is a simplified example, the real code has some redux-saga side effects (like select, put, etc)

How can I mock behaviour1?
Is there a better way to test chooseCorrectGenerator other than mocking behaviour1?