text: const counter = (state = 0, action) => {
      switch (action.type){
          case 'INCREMENT':
           return state+1;
          case 'DECREMENT':
            return state-1;
          default:
            return state;
      }
  }
  
  expect(
      counter(0, {type: 'INCREMENT'})
  ).toEqual(1);
  
  expect(
      counter(1, {type: 'INCREMENT'})
  ).toEqual(2);
  
  expect(
      counter(2, {type: 'DECREMENT'})
  ).toEqual(1);
  
  expect(
      counter(5, {type: 'DECREMENT'})
  ).toEqual(4)
  
  console.log('Tests passed!!!')