TestConvenienceFunctions violated AX Principle 1 (predictable names — "ConvenienceFunctions"
is a vague label, not a description of what is tested) and Principle 10 (test naming must
follow TestFilename_Function_{Good,Bad,Ugly}).
Renamed to TestProtocol_DefaultHandler_Good, added a usage-example doc comment per
Principle 2.
Co-Authored-By: Charon <charon@lethean.io>
Replace fmt.Errorf with a local testErr type to eliminate the banned
fmt import. The type carries its own usage example comment per AX
Principle 2.
Co-Authored-By: Charon <charon@lethean.io>