assert: throw real error in doesNotThrow()

[mscdex]

• Version: all?
• Platform: n/a
• Subsystem: assert

Currently assert.doesNotThrow() does not actually throw or otherwise give the message/content of the unexpected error. Instead it just throws a 'Got unwanted error' error, which isn't really helpful. It would be nice to either throw the seen error instead (preferred) or at the very least attach the unexpected error as a property on the thrown error.

[Trott]

If it throws the passed function's error instead, then is assert.doesNotThrow(fn) any different in effect from fn()? (That doesn't mean we shouldn't make this change. Just trying to get clarity.)

[refack]

IMHO it fits with #12820, we should wrap the original error in an AssertionError and provide a full stack trace. I'll follow up on this.

[BridgeAR]

The alternative version got implemented in c53db1e.
I guess this can be closed?