These tests were very simple before and now this should result
in more code coverage without affecting test performance.
The only tricky thing was testing the `--missing` option without
actually installing a package using `install_test_formula` because
that is very slow (around 10 seconds on my machine). I ended
up just writing the tab to a plausible keg directory for each
package I wanted to "install". This allows us to test the behavior
while also not increasing CI time by ~20 seconds (though it'd
probably be faster on CI than my local machine).
5c41e85ae9