test: include expected result in error messages

PR-URL: https://github.com/nodejs/node/pull/16039


Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>