Action don't change the state on reducer test with jest

I'm trying to test my reducer, but my initial state don't change when I dispatch an action on the test.

That's my reducer:

    export default function login(state = INITIAL_STATE, action) {
  switch (action.type) {
    case Types.SET_ERROR:
      return {
        ...state,
        error: action.error,
      };
    case Types.SET_LOGIN:
      return {
        ...state,
        user: {email: action.user.email, password: action.user.password},
      };
    default:
      return state;
  }
}

That's my test:

it('should handle SET_ERROR', () => {
      const setErrorAction = {type: 'SET_ERROR', error: 'a'};
      expect(login(INITIAL_STATE, setErrorAction)).toEqual({
        ...INITIAL_STATE,
        error: 'a',
      });
});

And that's my test result:

 expect(received).toEqual(expected) // deep equality

    - Expected
    + Received

      Object {
    -   "error": "a",
    +   "error": "",
        "user": Object {
          "email": "",
          "password": "",
        },
      }