Cannot ready property Calls of undefined

Question

In the above code block dispatcher is required and after register the mock function is giving as undefined.

describe('testStore', () => {
    // runs before each Test case.
    beforeEach( () => {  
       dispatcher = require('../../dispatcher').default;
    });  
    // Example test case
    it('test1', () => {
       expect(dispatcher.register.mock.calls.length).toBe(1);
    });
});