PR proposal: METEOR_TEST_PACKAGES env var flag when running meteor test-packages?

[Ronen Babayoff]

Hey,

There are certain use cases where it will be valuable to have this flag to be able to know if my package is running in the context of test-packages. A couple of use cases we ran into:

1. If a non-webapp package wants to define and export a main, such as our mcli (https://atmospherejs.com/practicalmeteor/mcli) package for creating meteor command line programs, this flag will allow me to not export the main in the context of test-packages, since main is already defined in webapp which is required for meteor test-packages to work with test-in-browser.

2. To be able to write unit tests for packages such as test-in-console, test-in-browser, and our upcoming mocha-web-driver test-packages driver.

Can I create a PR for that?

Thanks,

Ronen