问爬虫是什么原理？

import React from 'react'
import MyModal  from './MyModal'
import { mount, ReactWrapper } from 'enzyme'

it('renders correctly', () => {
    const wrapper = mount( <MyModal modalOpen/> );

    expect(wrapper).toMatchSnapshot();

    // Passes
    expect(wrapper.find('.outside')).toHaveLength(1);

    // Construct new wrapper rooted at modal content
    inside_els = document.getElementsByClassName("inside")[0]
    inside_wrapper = new ReactWrapper(inside_els, true)

    // Passes
    expect(inside_wrapper.find('.inside')).toHaveLength(1);
});

afterEach(() => {
  var node = global.document.body;
  while (node.firstChild) {
    node.removeChild(node.firstChild);
  }
});