Redux: Writing a Todo List Reducer (Toggling a Todo)

redux.js

const todos = (state=[], action) => {
  switch (action.type) {
    case 'ADD_TODO':
      return [
        ...state,
        {
          id: action.id,
          text: action.text,
          completed: false
        }
      ];
      
    case 'TOGGLE_TODO':
      return state.map(
        todo => {
          if (todo.id != action.id){
            return todo;
          }
          
          return {
            ...todo,
            completed: !todo.completed
          };
        }
      )
    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(stateAfter);
  
  expect (
    todos(stateBefore, action)
  ).toEqual(stateAfter);
  
};

const testToggleTodo = ()=> {
  const stateBefore = [
    {
      id: 0,
      text: 'Learn Redux',
      completed: false
    },
    {
      id: 1,
      text: 'Go shopping',
      completed: false
    }
  ];
  const action = {
    type: 'TOGGLE_TODO',
    id: 1
  };
  const stateAfter = [
    {
      id: 0,
      text: 'Learn Redux',
      completed: false
    },
    {
      id: 1,
      text: 'Go shopping',
      completed: true
    }
  ];
  
  deepFreeze(stateBefore);
  deepFreeze(stateAfter);
  
  expect(
    todos(stateBefore, action)
  ).toEqual(stateAfter);
};

testAddTodo();
testToggleTodo();
console.log('Passed');