clever way to test that `.metrics` was loaded. I like, though for clarity, can we either

*  add a comment here and  in the .metrics file that these lines are for testing?  I intend the `.metrics` file to be used as a template
* or perhaps not rely on setting a constant?  You could achieve a similar goal by having `METRIC_FILE_LOADED = {}` and then check that the hash was modified to e.g. `{:loaded => true}` to avoid the issue of redefining the constant. A $global variable would probably work equality well here.