Handle thrown values that are not Errors

[DmitrySharabin]

Closes #183.

Throwing a non-Error is legal JS, and real code does it. hTest crashed on it — and took the whole run down, not just the offending test. What the issue reported as one crash is five symptoms of one assumption: that the caught value is an object.

#	Site	Symptom
1	if ("actual" in e)	in throws on a primitive receiver
2	e.source = "beforeAll" (5 hook catches)	strict mode: cannot set a property on a primitive
3	pass: !!this.error	throws: false passed for a test that threw null
4	!("actual" in this.error)	crash when no throws criterion is set
5	${this.error.stack}	crash on throw null; phantom undefined line otherwise
6	${e.message} in the map()/check() catches	reports map() failed. undefined

#3 is the one to worry about: a silent false negative, not a crash.

The change

Normalize where the value enters, rather than teaching five downstream sites to cope with primitives:

export function asError (value) {
	return Object(value) === value ? value : new Error(String(value), { cause: value });
}

plus one e = asError(e); in each catch block. Every existing line in those blocks is untouched: with the value normalized up front, e.source = …, ${e.message}, "actual" in e and ${this.error.stack} all work as written.
Nothing else moves — "actual" in e, !!this.error and ${this.error.stack} stay exactly as they were, because with an object they were never wrong.

The original value survives as cause, so a predicate can still match it:

{ run () { throw "boom"; }, throws: error => error.cause === "boom" }

Verification

126/126. Each new test was confirmed red against the unfixed code, and the set was reduced by mutation testing: two candidates that never failed alone across six mutations (including a "guard the in sites instead of wrapping" alternative implementation) were dropped as subsumed.

Case	Before	After
throw "boom" | 42 | null | undefined, throws: true	crash	PASS
throw null, throws: false	passed	FAIL
throw "boom", no throws	crash	Got error Error: boom
beforeAll/beforeEach/afterEach throws a string	crash	SKIP, beforeEach: boom
throws: TypeError with a real Error	PASS	PASS, stack intact
check() that throws an Error	Got error Error: check() failed	unchanged
map()/check() that throws a string	map() failed. undefined	map() failed. mapboom

Diff stats

Substantive lines only (blank- and comment-only changes excluded).

File	Added	Removed
src/util.js	3	0
src/classes/TestResult.js	19	13
tests/errors.js	58	0
SKILL.md	1	1

Notes

• Output now reads Got error Error: boom rather than Got error boom, and throws: e => e === "boom" becomes e.cause === "boom". Both are new ground — the old behavior was a crash.
• asError lives in src/util.js by the file's own precedent: it holds single-consumer helpers (interceptConsole is used only by TestResult.js, regexEscape only by map.js), and the criterion is whether a helper knows anything about its caller. This one doesn't.
• SKILL.md's throws row now records that a non-Error is wrapped and the original is on .cause, per the project's SKILL.md-review rule for TestResult.js.
• Out of scope, pre-existing: a frozen Error thrown from a hook still crashes on e.source = …. Unchanged from main, not part of Throwing a non-Error crashes the runner and takes down the whole run #183.

🤖 Generated with Claude Code

https://claude.ai/code/session_01RaXmFiBg3UGUMuGFXjn5Ki

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[LeaVerou]

Can we add a property to the Error object that we are creating (or just make it our own subclass) so that we know to unwrap it instead of falsely reporting that an Error was thrown when it wasn't?