The title of this issue is the crux. It appears that the default spec reporter uses console.log rather than the built-in process.stdout that other reporters use. And there doesn't seem to be a pattern to which reporters use which output method.

Some reporters like spec (https://github.com/mochajs/mocha/blob/master/lib/reporters/spec.js#L40) are using console.log, some like dot(

My use case involves utilizing headless chrome to run mocha tests. I'm providing a proxy to window.mocha.process.stdout to use a message bus that I've injected, that pipes raw messages back to the node app which catches them via the Chrome DevTools Protocol. It might sound complex, but it's rather simple. Without knowing which actor (user code or mocha) is calling console.log, I can't effectively show console messages in the terminal with any distinction between actors.

The "simple" fix would be to standardize all reports on one output method - preferably mocha.process.stdout.