async_field.js

import React, { Component } from 'react'
import PropTypes from 'prop-types'

export class AsyncModelField extends Component {
  renderChild= () => {
    // This function effectively hooks onChange on our children by cloning and merging new props.
    // ASSUMPTION: this.props.children is actually just one child.  You can map this across many though.
    return React.cloneElement(this.props.children, {
      onChange: function() {
        // call ours
        this.handleChange(...arguments)

        // and if the child had one, call that too
        if (this.props.children.props.onChange) {
          this.props.children.props.onChange(...arguments)
        }
      }.bind(this),
    })
  }

  handleChange(value, errors) {
    console.log(value, errors)
  }

  render() {
    return <div>
      { this.renderChild() }
    </div>
  }
}

async_field.spec.js

import React from 'react'
import {shallow} from 'enzyme'
import chai, {expect} from 'chai'
import sinon from 'sinon'

import {AsyncModelField} from '../async_field'

describe.only('AsyncModelField component', function() {
   it('should transparently bind its own handleChange to child\'s onChange', function() {
    const spy = sinon.stub(AsyncModelField.prototype, 'handleChange')
    const original = sinon.spy()

    const wrapper = shallow(
      <AsyncModelField><input onChange={original} /></AsyncModelField>
    )
    const instance = wrapper.instance()

    wrapper.find('input').prop('onChange')('foo', [])
    expect(spy).to.have.been.calledWith('foo', [])
    expect(original).to.have.been.calledWith('foo', [])
  })
})

React stunt: Hook into your child's callbacks.