Why does adding a subdirectory (with test executables) in my CMakeLists cause my dll signature to get mismatched with my pdb signature?

Question

My library is organised like so :

lib/
├── src/
│   ├── code..
├── tests/
│   ├── code..
│   └── CMakeLists.txt
│
└─ CMakeLists.txt

The outer cma