Create the "equalMarkup" assertion

[pomek]

📝 Provide a description of the improvement

We already have the assertEqualMarkup() util for comparing markups.

ckeditor5/packages/ckeditor5-utils/tests/_utils/utils.js

Lines 148 to 172 in 2b1ea1a

	/**
	* An assertion util test whether two given strings containing markup language are equal.
	* Unlike `expect().to.equal()` form Chai assertion library, this util formats the markup before showing a diff.
	*
	* This util can be used to test HTML strings and string containing serialized model.
	*
	* // Will throw an error that is handled as assertion error by Chai.
	* assertEqualMarkup(
	* '<paragraph><$text foo="bar">baz</$text></paragraph>',
	* '<paragraph><$text foo="bar">baaz</$text></paragraph>',
	* );
	*
	* @param {String} actual An actual string.
	* @param {String} expected An expected string.
	* @param {String} [message="Expected two markup strings to be equal"] Optional error message.
	*/
	export function assertEqualMarkup( actual, expected, message = 'Expected markup strings to be equal' ) {
	if ( actual != expected ) {
	throw new AssertionError( message, {
	actual: formatMarkup( actual ),
	expected: formatMarkup( expected ),
	showDiff: true
	} );
	}
	}

However, many of us may do not know about the helper. Also, it requires adding additional imports.

We could add a new function to chai (https://www.chaijs.com/guide/helpers/#adding-methods) that will introduce the new assertion. The goal is to have something like this:

expect( editor.getData() ).to.equalMarkup( /* ... */ );

In details, the function will use the assertEqualMarkup() helper.

It would be nice to add the new helper to existing bindings to have the new assertion in IDE autocomplete list.

---

If you'd like to see, this improvement implemented, add a 👍 reaction to this post.

[pomek]

Scope:

• Create a new mocha assertion.
• Replace existing equalMarkup functions with the created assertion.

[przemyslaw-zan]

Normaly, you'd have to import this new assertion to use it within tests. However, there is a way of avoiding that - any new chai assertions can be imported in this file - after that, they are available in all tests.

attribute.js is an example of already existing custom chai assertion that has to be imported manually whenever needed. Do we want to move that to ckeditor5-dev-tests and include it in automatic import for all tests, so that there is no need to import that whenever needed? 

There might be other custom chai assertions that i'm not aware of, that also could be moved there.

[pomek]

attribute.js is an example of already existing custom chai assertion that has to be imported manually whenever needed. Do we want to move that to ckeditor5-dev-tests and include it in automatic import for all tests, so that there is no need to import that whenever needed? 

Wow. I wasn't aware of this. Yes, let's move all custom assertions to ckeditor5-dev-tests and enable using them in any test without importing it directly.

[przemyslaw-zan]

It would be nice to add the new helper to existing bindings to have the new assertion in IDE autocomplete list.

We ended up skipping that part, so perhaps it could be extracted to a followup?