JS Bin// source http://jsbin.com/cequnu

Redux: writing a todo list reducer final

const todos = (state=[], action) => {
  switch (action.type) {
    case 'ADD_TODO':
      return [
        ...state,
        {id: action.id,
        text: action.text,
        completed: false
        }
      ];
    default:
      return state;
  }
};

const testAddTodo = () => {
  const stateBefore = [];
  const action = {
    type: 'ADD_TODO',
    id: 0,
    text: 'Learn Redux'
  };
  const stateAfter = [
    {
      id: 0,
      text: 'Learn Redux',
      completed: false
    }
  ];
  
  deepFreeze(stateBefore);
  deepFreeze(action);
  
  expect(
    todos(stateBefore, action)
  ).toEqual(stateAfter);
};

testAddTodo();

console.log('Tests passed');