test_runner: add snapshot testing

[cjihrig]

test_runner: add context.fullName

This commit adds a fullName getter to the TestContext and
SuiteContext classes. This is similar to the existing name getter,
but also includes the name of all ancestor tests/suites.

doc: add context.assert docs

When context.assert was added, no docs were added. This commit
adds initial documentation for context.assert because the
snapshot() function requires them.

Refs: #52860

test_runner: add snapshot testing

This commit adds a t.assert.snapshot() method that implements
snapshot testing. Serialization uses JSON.stringify() by default,
but users can configure the serialization to meet their needs.

Fixes: #48260

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[benjamingr]

@targos

[benjamingr]

Nice work, good tests, left some comments, want to see how people feel about this but personally I'm +1

[JakobJingleheimer]

I believe snapshot does not belong in core because it's too specific to a domain.

[Chamindu36]

@cjihrig It seems like this is missing backtick consistency for string values in snapshots.

[cjihrig]

I'm not sure what you mean.

[cjihrig]

I believe snapshot does not belong in core because it's too specific to a domain.

I think this is a little too vague. What domain? What can't we do that most other test runners have figured out how to do?

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/59493/

[DylanPiercey]

@cjihrig is there any reason JSON.stringify was chosen here over util.inspect? The inspect api supports a bunch more data types, circular properties, and allows defining custom overrides.

Seems like it'd be a good fit here?

[cjihrig]

Yes. Per the util.inspect() docs:

The output of util.inspect may change at any time and should not be depended upon programmatically.

It's not a suitable default for Node core, but you can use it for your own serialization if you want.

[DylanPiercey]

Ah, lame. Alright, thanks for the heads up!

It'd be nice if the stance was changed on that api to only change output across majors. It seems reasonable to me that you might have to update your snapshots when upgrading to a new major. Oh well!

[cjihrig]

I would also love to see someone get a better and reliable serialization format in place!

[benjamingr]

util.inspect was actually used in the past iteration of snapshot testing we had and it caused problems people complained about (about how it defines equality and semverness)

[ChALkeR]

Looking at that code, this method appears duplicated:

node/lib/internal/test_runner/test.js

Lines 1236 to 1244 in e08a654

	function getFullName(test) {
	let fullName = test.name;
	for (let t = test.parent; t !== t.root; t = t.parent) {
	fullName = `${t.name} > ${fullName}`;
	}
	return fullName;
	}

node/lib/internal/test_runner/test.js

Lines 228 to 230 in e08a654

	get fullName() {
	return getFullName(this.#test);
	}

Could be simplified with

node/lib/internal/test_runner/test.js

Lines 546 to 550 in e08a654

	getTestNameWithAncestors() {
	if (!this.parent) return '';
	return `${this.parent.getTestNameWithAncestors()} ${this.name}`;
	}

I.e. the test could have just had a .getPath which was joined with different strings likely? Perhaps I'll recheck