Fix tests in case-sensitive file system

[Qusic]

Replaced IMessage with iMessage in test project files (to be consistent with project.yml).
Also use some different names to enforce renaming on case-insensitive file systems.

[keith]

Moving these files will break this repo in case insensitive file systems. Doing a git pull won't work.

[Qusic]

I agree. But when I cloned this repo, the tests did fail to run. Do you have any suggestions to fix that?

[Qusic]

Updated names in project.yml this time. It works for me and I think it shouldn't break tests elsewhere.

[yonaskolb]

Thanks @Qusic!