Opening this as a question as I'm not yet sure whether it's a bug or a user error 😄

The docs on extending configuration state:

Configurations can inherit from other modules using the extends keyword

However, I've been unable to get this to work and I haven't been able to find any Mocha-specific examples leveraging extends. I've tried using extends both with a relative path to a json file, as well as with a module as referenced in the yargs docs linked from the Mocha docs, and I also tried the various Mocha config file formats (js, yaml, json, etc.) to define the Mocha config with the extends keyword, all to no avail.

I created a really simple repo here that reproduces this behavior:

ui should be set to tdd via the extends reference in the .mocharc.yml file, but running an npm test results in a reference error ReferenceError: suite is not defined leading me to believe that extends is not working since the ui is still set to the default bdd

Any help would be greatly appreciated!