feature: support IDOMElementDescriptors

[bendemboski]

Implement support for RFC #726

[bendemboski]

This PR does change existing error messages, as can be seen from the tests, which isn't an explicit goal of this change. Here's the explanation.

If an assertion couldn't find its element (whether because of a non-matching selector or because it was passed null), previously the error messaging would be inconsistent between its usage of <not found> vs. <unknown>. The code that produced those messages was refactored and is now driven by the dom element descriptor description functionality, so it would require extra code to restore the inconsistent behavior and keep the error message the same as it was before this PR.

[BobrImperator]

qunit-dom attempts to stay lean and it also promotes a way of testing without using page-objects. I understand the need and how its useful for some use cases.

I'd like us to look for a way for dom-element-descriptors to depend on qunit-dom instead and not the other way .around.
It seems like qunit-dom at the very minimum would need to provide a way to extend the element lookup and descriptions if they're required. and the assert.dom method.

Then what users of dom-element-descriptors would need to do is swap out qunit-dom setup with dom-element-descriptors setup.

// tests/test-helper.js
import * as QUnit from 'qunit';
import { setup } from 'dom-element-descriptors';

//...
setup(QUnit.assert);
setApplication(Application.create(config.APP));
start();
//...

Some pseudo code for potential qunit-dom extension could be:

import { setup, DOMHandler } from 'qunit-dom'

// A class or anything that implements similar interface
class DOMElementDescriptorHandler implements DOMHandler {
  findElement(selector, rootElement)
  findElements(selector, rootElement)
  description(selector)
  resultMessage()
}

setup(QUnit.assert, [new DOMElementDescriptorHandler()])

Draft #2101

[BobrImperator]

Drafted #2101 as per feedback, would this help dom-element-descriptors to create a "plugin" for qunit-dom?

[BobrImperator]

Please rebase the PR.

[bendemboski]

@BobrImperator this is rebased and, pending your decision on the assertion messages change or any other feedback you might have, ready to merge!

[BobrImperator]

https://github.com/mainmatter/qunit-dom/releases/tag/v3.2.0 🚀