Can't use --watch with mocha as it causes prometheus metric errors

[neilbmclaughlin]

When trying to use the --watch flag with mocha any file change results in a prometheus error of the form:

Error: A metric with the name http_request_duration_seconds has already been registered.

This issue describes the background to the problem but offers no solutions.

Needs further investigation.

[neilbmclaughlin]

Note: the yarn 'start-watch' script works OK on file change but that is using brunch watch and nodemon.