Fix duplication of mocha.opts on process.argv

[nexdrew]

Found by @jameswomack (see yargs issue 267), mocha is reading options from test/mocha.opts and adding them to process.argv twice - once in bin/mocha and then again in bin/_mocha. This PR removes the 2nd one and adds a unit test to cover this scenario.

Wasn't quite sure where to put the unit test, but test/integration/regression.js seems like a decent place.

Let me know if there's anything you'd like me to change. Thanks.

[danielstjules]

This could be an issue for those who invoke mocha using _mocha rather than the normal bin (unfortunate, but I've seen it a lot)

[nexdrew]

@danielstjules Hmm, ok. Would you recommend adding something to bin/options.js then, to check if mocha.opts has already been read/applied?

[danielstjules]

Could we keep it in _mocha, and remove the duplicate from mocha instead?

[danielstjules]

Woops, sorry! :) Having a slow morning

[nexdrew]

@danielstjules Yeah, that should work. I will fix and push soon.

[nexdrew]

@danielstjules Should be good now, I think.

[nexdrew]

Any more feedback on this?

[jameswomack]

LGTM 🚢 🇮🇹

[nexdrew]

Looks like there are several PRs stuck in limbo. Anything I can do to help?

[travisjeffery]

Could've sworn there was a reason they were duplicated, but perhaps not.

[nexdrew]

@travisjeffery Thanks!

[mattfysh]

thanks for the fix :) any idea when this will be published to npm?