React - Enzyme test - simulating change return undefined

I'm new in React Enzyme testing. I want to simulate input/change action.

Second test failed although input '#num1' is found:

Expected value to equal: "23"
Received: "undefined"

I tried using 'text()' instead of 'value', then return "".

Also I wrote a test which look for button text and passed return '+'.

When I remove one of two inputs and find 'input', also return 'undefined'.

App.js

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';

class App extends React.Component{
        constructor(){
            super();
            this.state = {
                number1: 0,
                number2: 0,
                result: 0
            }
        }

        render(){
            return(
            <div>
                <div>
                    <label>Number 1</label>
                    <input id="num1" onInput={this.rememberNumber1.bind(this)} />
                    <br/><br/>
                    <label>Number 2</label>
                    <input id="num2" onInput={this.rememberNumber2.bind(this)} />
                </div>
                <div>
                    <h1>{this.state.number1}+{this.state.number2}={this.state.result}</h1>
                </div>
                <div>
                    <button id="an" onClick={this.sum.bind(this)}>+</button>
                    <button onClick={this.subtract.bind(this)}>-</button>
                    <button onClick={this.multiply.bind(this)}>*</button>
                    <button onClick={this.divide.bind(this)}>:</button>
                </div>
            </div>
            )
        }

        rememberNumber1(e){
            if (e.target.value==""){
                this.setState({
                    number1: 0
                })
            }
            else {
                this.setState({
                    number1: e.target.value
                })
            }
        }

        rememberNumber2(e){
            if (e.target.value==""){
                this.setState({
                    number2: 0
                })
            }
            else {
                this.setState({
                    number2: e.target.value
                })
            }
        }

        sum(e){
            this.setState({
                result: Number(this.state.number1)+Number(this.state.number2)
            })
        }

        subtract(e){
            this.setState({
                result: Number(this.state.number1)-Number(this.state.number2)
            })
        }

        multiply(e){
            this.setState({
                result: Number(this.state.number1)*Number(this.state.number2)
            })
        }

        divide(e){
            this.setState({
                result: Number(this.state.number1)/Number(this.state.number2)
            })
        }
}
export default App;

setupTests.js

import React from 'react';
import { shallow, mount } from 'enzyme';
import App from './App';

import { configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';

configure({ adapter: new Adapter() });

it('includes input', () => {
    const app = shallow(<App />);
    expect(app.containsMatchingElement(<input/>)).toEqual(true)
});

it('on input', () => {
    const wrapper = mount(<App />);
    wrapper.find('#num1').simulate('change', {target: {value: 23}})
    expect(wrapper.find('#num1').value).toEqual('23')
});