feature request: fail if no test functions are run

If you run nodeunit on an empty directory, it just prints
OK: 0 assertions
and exits successfully.

It would be nice if this exited with an error status code by default. That way, the build will fail if you move the tests and forget to update the nodeunit invocation.

(The workaround is to use a custom reporter)

Start by tracing the nodeunit invocation and default reporter behavior when an empty directory produces zero assertions. Check how the custom reporter workaround determines failure, then add coverage for the default behavior and verify that a no-test run exits unsuccessfully while normal test runs still pass.

Written by the indexing model from the issue text.