test: address nits and rename the corresponding fixture

Refs: https://github.com/nodejs/node/issues/19105

PR-URL: https://github.com/nodejs/node/pull/19161
Refs: https://github.com/nodejs/node/blob/master/doc/guides/writing-tests.md#test-structure


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>