reducer-0.spec.js

const reducer = require('./reducer-0');

describe('reducer()', () => {
  it('should handle increment and decrement actions', () => {
    expect(reducer({ type: 'INCREMENT' })).toEqual({ count: 1 });
    expect(reducer({ type: 'INCREMENT' })).toEqual({ count: 2 });
    expect(reducer({ type: 'DECREMENT' })).toEqual({ count: 1 });
  });

  it('should depend on prevous invocations (history) - unpredictable!', () => {
    // El estado va a depender de si se ha ejecutado el test
    // anterior o no!!
    expect(reducer({ type: 'INCREMENT' })).toEqual({ count: 2 });
  });
});