Add support for --test

[bbqsrc]

Hey @TimNN,

I've recently mangled together some xcrun simctl functionality to run tests, and was wondering if you're be open to a PR that implements something similar but more integrated into cargo lipo?

It may be that we still need something like https://github.com/carllerche/ios-test-harness for longer running tests, especially if a real device is involved.

In any case, please at least let me know if this is something that would interest you or if I should make it as a separate crate. 😄

[simlay]

@bbqsrc That's some cool xcrun simctl mangling you did. You might wanna try out dinghy. I added iOS simulator support like about a year ago. They run the tests for dinghy in CI for the iOS simulator.

[TimNN]

I think this is out of scope for cargo lipo, and might be better served with a more general cargo xcode or cargo ios subcommand.

(Somewhat unrelated, but if I was doing Rust / iOS development these days, I probably wouldn't use lipo at all (neither directly nor via cargo-lipo), but rather a setup like the one I briefly described on reddit some time ago. Although an --xcode-integ like utility would probably still be very useful).