Write e2e tests

[kentcdodds]

As suggested by @nkbt in #30. Maybe we could use nixt.

[nkbt]

I'll take it. Want to try nixt as it looks pretty sick. Hopefully will get some base tests out later today

[kentcdodds]

Sweet. I've never used nixt. Looking forward to what you come up with!

[nkbt]

Hm nixt does not seem to work properly for me. Spent a bit of time with it, but no luck yet.

vesln/nixt#16

Maybe I will go with bash then for the moment, or look for some nicer alternative... Not today tho

[kentcdodds]

Cool. See if you can make it work cross-platform so we don't shut out windows users.

[nkbt]

That might be a concern, though I expected to run e2e on CI to begin with. Generally I doubt it is possible to do completely cross-platform CLI testing, since shell scripts will be running in background anyway =(.

[kentcdodds]

Makes sense. I think we're OK if it's only running in CI

[nkbt]

Since nixt is not really working and writing shell scripts at home on my Windows was not an easy option, I fixed a cli-tester. Not particularly a rocket science thingy...

Had some fun making it work smoothly on all Node versions down to 0.10 (so it is ok with p-s matrix build).

Welcome =)

[kentcdodds]

Cool! Looking forward to seeing the pull request!