Exit with a nonzero status if we get an error

[carols10cents]

A branch of the book had a code example that failed with mdbook test, but travis reported a success. This is because the exit status of mdbook test (and other commands) is still 0 even when there are errors.

I made a little repo that has an example to test with, but the book-example in this repo also currently has an error with mdbook test 😱

Before this patch, if I run mdbook test on those, I get an exit status of 0 when I expect to get nonzero. After this patch, I get the nonzero exit status that I expected (I went with 101 because that's what rustdoc --test returns if it fails), and I continue to get an exit status of 0 when running mdbook test on a book that passes its tests.

This does affect all commands. I'm not sure if others were already exiting as expected when encountering errors or not. It looks like watch might.

I didn't see any automated tests that actually run the binaries-- please point me to the appropriate place to add tests if I missed them!

[azerupi]

Thanks! This was indeed a huge oversight.

I didn't see any automated tests that actually run the binaries

No, I have not much experience with writing good tests and it's an area that is definitely lacking in this project. At some point I should take the time to write a good test suite. But in the mean time, if you feel like adding a test for this, I'm not gonna stop you 😉