React A11y Testing

enzyme-test.js

import {expect} from 'chai';
import App from '../app/components/App';

import a11yHelper from "./a11yHelper";

describe('Accessibility', function () {
  this.timeout(10000);

  it('Has no errors', function () {
    let config = {};
    // let config = {
    //   "rules": {
    //     "color-contrast": { enabled: false }
    //   }
    // };
    a11yHelper.testEnzymeComponent(<App/>, config, function (results) {
      expect(results.violations.length).to.equal(0);
    });
  });
});

reactA11yHelper.js

import React from 'react';
import {findDOMNode, render} from 'react-dom';
import {mount} from 'enzyme';
import axeCore from 'axe-core';

var a11yHelper = {};

/**
 * Test a component with React's Test Utils.
 *
 * @param {any} app - Your app reference.
 * @param {object} config (optional) - An aXe config object to enable/disable rules. See 
 * [axe.a11yCheck](https://github.com/dequelabs/axe-core/blob/master/doc/API.md#options-parameter).
 * @param {function} callback - A callback function to execute when aXe returns.
 */
a11yHelper.testReactComponent = function(app, config, callback) {
	let div = document.createElement('div');
	document.body.appendChild(div);
	this.wrapper = render(app, div);

	let node = findDOMNode(div);

	if (typeof config === 'function') {
		config = {};
	}
	this.run(node, config, callback);

	document.body.removeChild(div);
}
/**
 * Test a component with Enzyme.
 *
 * @param {any} app - Your app reference.
 * @param {object} config (optional) - An aXe config object to enable/disable rules. See 
 * [axe.a11yCheck](https://github.com/dequelabs/axe-core/blob/master/doc/API.md#options-parameter).
 * @param {function} callback - A callback function to execute when aXe returns.
 */
a11yHelper.testEnzymeComponent = function (app, config, callback) {
	let div = document.createElement('div');
	document.body.appendChild(div);
	
	let wrapper = mount(app, { attachTo: div });
	let node = findDOMNode(wrapper.component);

	if (typeof config === 'function') {
		config = {};
	}
	this.run(node, config, callback);
	document.body.removeChild(div);
}
/**
 * Run an aXe audit.
 * @private
 *
 * @param {object} node - A node reference from your app.
 * @param {object} config - An aXe config or empty object.
 * @param {function} callback - A callback function to execute when aXe returns.
 */
a11yHelper.run = function(node, config, callback) {
	var oldNode = global.Node;
	global.Node = node.ownerDocument.defaultView.Node;

	axeCore.run(node, config, function(err, results) {
		global.Node = oldNode;
		
		if (err instanceof Error) {
			return err;
		}

		a11yHelper.report(results);
		
		// return to the test expectation
		callback(results);
	});
}
/**
 * Report results in a readable fashion.
 * @private

 * @param {object} results - The aXe [results object](https://github.com/dequelabs/axe-core/blob/master/doc/API.md#results-object).
 */
a11yHelper.report = function(results) {
	// output some useful information
	let failureNotice = '';
	if (results.violations.length > 0) {
		failureNotice += 'Accessibility violations:\n';
		results.violations.forEach(function(violation) {
			failureNotice += violation.description + '\n';
			failureNotice += 'HTML Nodes: \n';
			violation.nodes.forEach(function(node) {
				failureNotice += node.html + '\n';
			});
		});
		console.log(failureNotice);
	}
}
module.exports = a11yHelper;

What is global.Node and why is it being set to node.ownerDocument.defaultView.Node?

I changed line 43 to let node = wrapper.getDOMNode(); and then this worked! Thanks Marcy.