deleteTodo.js

function deleteTodo(text) {
  return {
    type: DELETE_TODO,
    text: text
  };
}

const initialState = []

function todoReducer(state = initialState, action) {
  switch(action.type) {
  case(DELETE_TODO):
    return _.filter(todos, (todo) => todo.text = action.text);
  }
}

describe('deleting a todo', () => {
  describe('when there are no todos', () => {
    const state = [];

    it('returns the state unchanged', () => {
      assertEqual(todoReducer(state, deleteTodo('foo')), state)
    });
  });

  describe('when the todo exists alone', () => {
    const theTodo = { text: 'foo' };
    const state = [theTodo];

    it('removes the todo', () => {
      const newState = todoReducer(state, deleteTodo('foo'));

      assert(!_.includes(newState, theTodo));
    });
  });

  describe('when the todo exists with other todos', () => {
    const firstTodo = { text: 'foo' };
    const secondTodo = { text: 'bar' };
    const state = [firstTodo, secondTodo];

    it('removes the target todo', () => {
      const newState = todoReducer(state, deleteTodo('foo'));

      assert(!_.includes(newState, firstTodo));
    });

    it('leaves the other todos', () => {
      const newState = todoReducer(state, deleteTodo('foo'));

      assert(_.includes(newState, secondTodo));
    });
  });
});