React Props Mounted

We have several major goals in this assignment. To learn how to:

  • Test Nested components with Enzyme shallow and mount
  • Test with Enzyme shallow and mounted
  • Look at a logger


There are some very good loggers out there, and we should probably be using those. Still, there is perhaps some value in writing our own loggers. If nothing else, they show us why the best loggers are so good. The key trait we want in a logger is the ability to turn logging on and off. The issue, of course, is that sometimes console.log statements are very useful, and sometimes they just get in the way. Being able to turn them on and off is useful.

This is still a bit tentative, but here is a useful, if somewhat naive, simple logger. I’ve saved it in my src directory as elf-logger.js:

 * Created by charlie on 4/18/17.

  * Created by charlie on 4/18/17.

 const ElfLogger = class {

     constructor(initQuiet) {
         this.display = initQuiet;
         this.log = this.log.bind(this);
         this.setQuiet = this.setQuiet.bind(this);

     log(message1, message2 = '', message3 = '') {
         if (this.display) {
             console.log(message1, message2, message3);

     setQuiet(newValue) {
         this.display = newValue;

 export default ElfLogger;

Use it like this, where the boolean in the second line turns the logger on or off:

import Logger from '../elf-logger';
const logger = new Logger(false);

logger.log('Logging now');

As you can see, the logger can accept up to three parameters.

NOTE: When I get time, I’d like to have the logger work depending on whether or not an environment variable is set, as that is more flexible than this module by module approach:

if (process.env.SERVERFOO) {
  console.log(message1, message2, message3);

Enzyme shallow and mount

Before going further, read this section from Elvenware:

Testing Elements with Complex Attributes {#on-change=attrs}

In our code so far, we have always been attempting to match exactly and completely what is rendered by an HTML element. For instance, we have written code like this:

const fooState = <p className="App-intro"> bar</p>;

Here we are expecting our paragraph element to more or less exactly match the string we assign to fooState. However, there are times when the controls we create are more complex than this. On some of these of these occasions, it is, at best, difficult to compose a string that exactly matches our controls output.

In particular, suppose your code produces a control that is reported by Enzyme to render like this:

<input value="Robin Dudette" onChange={[Function]} />

Note the onChange attribute, and the react expression to which it is equated. It turns out that such code is hard to match.

In such cases you might consider writing test code like this:

import { mount } from 'enzyme';

function getLast(wrapper, element) {
    const eightp = wrapper.find(element).last().debug();
    logger.log("GETUSERINFO TEST GET LAST:", eightp);

  * @param {object} wrapper - Container for a bunch of HTML nodes
  * @param {number} index - Index of HTML element in the wrapper
  * @param {boolean} talkToMe - Speak even if quiet is true
 const getIndex = function(wrapper, index, talkToMe) {
     if (!quiet || talkToMe) {
         const ninep = wrapper.find('div#addressShowRender').childAt(index).debug();
         console.log('NINEP:', ninep);

it.only('renders button click message for state.userLogin', () => {
    const wrapper = mount(<GetUserInfo />);
    const inputElement = <input value="Robin Dudette" />;
    getLast(wrapper, 'input');

Your getLast debug method may report that your HTML control is generating something like this:

<input value="Robin Dudette" onChange={[Function]} />

Yet testing for that exact string seems to fail no matter what I do, probably because [Function] is being expanded to something more than what is shown here. After doing some research, I found it was easier to use containsMatchingElement instead of contains.

Here was my first attempt to match that output:

const inputElement = <input value="Robin Dudette" onChange={[Function]} />

As you can see, I’m trying to mirror what I see in the Enzyme debug. It was a good try, I suppose, but it didn’t work. Instead, I ended up doing this:

const inputElement = <input value="Robin Dudette" />;

Note that I’m calling containsMatchingElement rather than contains. This turns out to be a more forgiving method. Even though the inputElement variable shown above does not exactly match the output of the control, it is close enough to pass the test, yet strict enough to catch obvious errors, such as value being set to something other than Robin Dudette.

Testing ShowUserInfo

When we test GetUserInfo we might want, in some cases, to use Enzyme’s mount because GetUserInfo has a child called ShowUserInfo. But ShowUserInfo appears at first to have no such child, so we can naively think it might be possible to test it with shallow. In fact, ShowUserInfo relies on ElfElements, which is a component. As a result, we should use mount if we want to check everything.

Testing ShowUserInfo:

describe('Show User Info mount Test', function () {

    let bodyData = {};

    beforeEach(function() {
        const tempBody = {};
        for (let value of fieldDefinitions) {
            tempBody[] = value.sample;

    it('renders without crashing', () => {
        const div = document.createElement('div');
            onChange={function() {&#125;&#125;
        />, div);

Testing GetUser Info

Read about ElfTestShow on Elvenware.

import { mount } from 'enzyme';
import ElfTestShow from '../ElfTestShow';
const elfShow = new ElfTestShow(false);

describe('My Get User Info test', function () {

    it('renders without crashing', () => {
        const div = document.createElement('div');
        ReactDOM.render(<GetUserInfo />, div);

Turn it in

Follow the instructions in ReactPropsShow. Call the branch: ReactPropsMounted. Or, if your code is in the ReactPropsShow branch, let me know. Something like this:

  • add, commit, push. When you commit, include a message that mentions the assignment name.
  • tag, push. When you tag, include a message that mentions the assignment name.
  • if you are not already in a branch named after your project, then create one: git branch ReactPropsMounted. Whether you ever enter and use the branch is up to you. To enter it: git checkout ReactPropsMounted.


shallow can see all the HTML tags in a render method, but it can’t see into the sub-components. Consider this code:

render() {
    if (!this.quiet) { console.log("ADDRESS RENDER"); }
    return (
        <div className="App">
            <MyAddress />

shallow can see that this render method contains a second React component called MyAddress, but it can’t see the render method of MyAddress. mount can see into MyAddress. This means it can find the list items or paragraphs that may be listed as part of the MyAddress react Component. In cases like that shown above, it can see the render method of MyAddress, but shallow cannot.

Just to be clear, it would not matter how many divs, list items, paragraphs or other tags were included in the render method shown above. shallow could see them all. But it could not see into the contents of the render method of MyAddress.