Stop huge error output from testing-library

Question

I love testing-library, have used it a lot in a React project, and I'm trying to use it in an Angular project now - but I've always struggled with the enormous error output, including the HTML text of the render. Not only is this not usually helpful (I couldn't find an element, here's the HTML where it isn't); but it gets truncated, often before the interesting line if you're running in debug mode.

I simply added it as a library alongside the standard Angular Karma+Jasmine setup.

I'm sure you could say the components I'm testing are too large if the HTML output causes my console window to spool for ages, but I have a lot of integration tests in Protractor, and they are SO SLOW :(.

Answer 1

I would say the best solution would be to use the configure method and pass a custom function for getElementError which does what you want.

You can read about configuration here: https://testing-library.com/docs/dom-testing-library/api-configuration

An example of this might look like:

configure({
  getElementError: (message: string, container) => {
    const error = new Error(message);
    error.name = 'TestingLibraryElementError';
    error.stack = null;
    return error;
  },
});

You can then put this in any single test file or use Jest's setupFiles or setupFilesAfterEnv config options to have it run globally.

Answer 2

I am assuming you running jest with rtl in your project.

I personally wouldn't turn it off as it's there to help us, but everyone has a way so if you have your reasons, then fair enough.

1. If you want to disable errors for a specific test, you can mock the console.error.

    it('disable error example', () => {

  const errorObject = console.error; //store the state of the object
  console.error = jest.fn(); // mock the object

  // code

  //assertion (expect)

  console.error = errorObject; // assign it back so you can use it in the next test
});

2. If you want to silence it for all the test, you could use the jest --silent CLI option. Check the docs

The above might even disable the DOM printing that is done by rtl, I am not sure as I haven't tried this, but if you look at the docs I linked, it says

"Prevent tests from printing messages through the console."

Now you almost certainly have everything disabled except the DOM recommendations if the above doesn't work. On that case you might look into react-testing-library's source code and find out what is used for those print statements. Is it a console.log? is it a console.warn? When you got that, just mock it out like option 1 above.

UPDATE

After some digging, I found out that all testing-library DOM printing is built on prettyDOM();

While prettyDOM() can't be disabled you can limit the number of lines to 0, and that would just give you the error message and three dots ... below the message.

Here is an example printout, I messed around with:

    TestingLibraryElementError: Unable to find an element with the text: Hello ther. This could be because the text is broken up by multiple elements. In this case, you can provide a function for your text matcher to make your matcher more flexible.

...

All you need to do is to pass in an environment variable before executing your test suite, so for example with an npm script it would look like:

DEBUG_PRINT_LIMIT=0 npm run test

Here is the doc

UPDATE 2:

As per the OP's FR on github this can also be achieved without injecting in a global variable to limit the PrettyDOM line output (in case if it's used elsewhere). The getElementError config option need to be changed:

dom-testing-library/src/config.js

     // called when getBy* queries fail. (message, container) => Error 
 getElementError(message, container) { 
   const error = new Error( 
     [message, prettyDOM(container)].filter(Boolean).join('\n\n'), 
   ) 
   error.name = 'TestingLibraryElementError' 
   return error 
 }, 

The callstack can also be removed

Answer 3

You can change how the message is built by setting the DOM testing library message building function with config. In my Angular project I added this to test.js:

configure({
  getElementError: (message: string, container) => {
    const error = new Error(message);
    error.name = 'TestingLibraryElementError';
    error.stack = null;
    return error;
  },
});

This was answered here: https://github.com/testing-library/dom-testing-library/issues/773 by https://github.com/wyze.