create goss test that passes (or not) based on exit code of bash command

Goss is a tool for validating server specifications. I have reviewed the documentation but I can't find a way to create a test that is based on the return code of a bash command. I'm looking for an example.

Also, as of early 2020, the goss repo has 3.6k stars on Github. Maybe someone with sufficient stackoverflow mojo could create a new tag to track goss related questions on StackOverflow.