Stubbing non-public method should use same visibility

[floehopper]

Maybe? Or maybe stubbing a non-public method is a code smell?

See https://github.com/ryanong/spy

[floehopper]

Stubbing a non-public method probably is a code smell, but given that it is possible, it would probably be less surprising if the stub had the same visibility as the original method.

Also we already cater for those who think it's a code smell, by providing the Mocha::Configuration.prevent(:stubbing_non_public_method) option.

Fixing this might break existing tests, so it probably requires at least a minor version increment, if not a major version increment (as per semantic versioning).