reducer-1.spec.js

const reducer = require('./reducer-1');

describe('reducer()', () => {
  it('should not be affected by previous calls', () => {
    expect(reducer(undefined, { type: 'INCREMENT' })).toEqual({ count: 1 });
    expect(reducer(undefined, { type: 'INCREMENT' })).toEqual({ count: 1 });
    expect(reducer(undefined, { type: 'DECREMENT' })).toEqual({ count: -1 });
  });

  it('should handle increment action', () => {
    const state1 = reducer(undefined, { type: 'INCREMENT' });
    const state2 = reducer(state1, { type: 'INCREMENT' });
    // Todas las referencias a state apuntan al mismo objeto que
    // hemos ido mutando!!!
    expect(state1).toEqual({ count: 2 });
    expect(state2).toEqual({ count: 2 });
    expect(state1).toBe(state2);
  });
});