let todo = (state = [], action) => {

  switch(action.type){

    case 'ADD_ITEM':

      return state = [

        ...state,

        {

          text: action.text,

          id: action.id,

          completed: false

        }

      ];

    case 'TOGGLE_ITEM':

      return state.map( (todo) => {

        if(todo.id !== action.id){

          return todo;

        }else{

         return {

          ...todo,

          completed: !todo.Completed// will overwirte the todo object's completed prop

        };

        }

      })

    default:

      return state;

  }

};

let testTodo_addItem = () => {

  let stateBefore = [];

  let action = {

    type: 'ADD_ITEM',

    text: 'Learn Redux',

    id: 0

  };

  let stateAfter = [

    {

      text: 'Learn Redux',

      id: 0,

      completed: false,

    }

  ];

  deepFreeze(stateBefore);

  deepFreeze(action);

  expect(

    todo(stateBefore, action)

  ).toEqual(stateAfter);

};

let testTodo_toggleItem = () => {

  let stateBefore = [

    {

      text: 'Learn Redux',

      id: 0,

      completed: false

    },

    {

      text: 'Learn Angular2',

      id: 1,

      completed: false

    }

  ];

  let action = {

    type: 'TOGGLE_ITEM',

    id: 1

  };

  let stateAfter = [

    {

      text: 'Learn Redux',

      id: 0,

      completed: false

    },

    {

      text: 'Learn Angular2',

      id: 1,

      completed: true

    }

  ];

  deepFreeze(stateBefore);

  deepFreeze(action);

  expect(

    todo(stateBefore, action)

  ).toEqual(stateAfter);

}

testTodo_toggleItem();

console.log("All tests passed!");