We're trying to find a problem with tests that use moment.js and fail when run on a server in Arizona but succeed when run locally here in the UK. We manually set the locale before creating a moment and can see that the local 'en-gb' is installed.
This fiddle highlights what I think the problem is (Need to set computer to Arizona Time zone first!) https://jsfiddle.net/2ve10ax4/
Locale and timezone are orthogonal things. A locale does not specify a timezone unambigously. You need to set your timezone separately. You can use Momemt Timezone, and then you can use e.g.