Fix test toggle for umbrella-based apps

[russmatney]

This has been bugging me for a while, finally got back around to digging into it today.

If there are other known umbrella-app related issues, I'd be happy to take a crack at them.

[rschmukler]

@tonini any chance on a merge / publish with this fix? We make pretty extensive use of umbrellas and this would be super helpful!

[tonini]

thanks @russmatney :green_heart: