Hey @plu!
Excited to hear that Kleinanzeigen is considering using Tuist 
As a Berliner, I use that app quite often 
And we’d like to generate a scheme for each of them, so the developers can easily execute tests.
There’s a PR to implement that behavior: https://github.com/tuist/tuist/pull/6436
We can try to take the PR over and finish it. Currently, you’d need to convert the SPM unit test targets to Tuist.
This means we want to stick to SPM for managing our local packages, and avoid describing each of them as Tuist targets, if that’s possible at all.
We generally recommend eventually migrating to Tuist as you won’t be able to get the full benefits of Tuist if you keep using local packages. If you feel strongly about keeping some targets defined using SPM, I’d consider at least moving to the XcodeProj-based integration by referencing them in the Tuist/Package.swift file.
You can book some time with us if you want to discuss the options in a call.