Jest throws an error " Received: serializes to the same string"

I'm testing my reducer. I have no idea where I'm making mistake. Could you please help me with that

case SET_CONFIRM_INFO:
      return {
        ...state,
        confirmFields: action.confirmFields,
        adding: (action.adding !== '') ? action.adding : [],
        checkInfo: action.checkInfo,
        getAddings: action.getAddings
      };

here is my test:

  it('SET_CONFIRM_INFO', () => {
    const action = {
      type: SET_CONFIRM_INFO,
      confirmFields: [1, 2, 4],
      adding: [1, 2, 3],
      checkInfo: { 1: 'a', 2: 'b' },
      getAddings: () => []
    }

    expect(pay(defaultState, action)).toEqual({
      ...defaultState,
      confirmFields: action.confirmFields,
      adding: action.adding,
      checkInfo: action.checkInfo,
      getAddings: () => []
    })
  })

and error: