Without it you'll get error like this:
CMake Error at api/nblib/CMakeLists.txt:79 (add_dependencies): Cannot add target-level dependencies to non-existent target "tests".
The add_dependencies works for top-level logical targets created by the add_executable, add_library, or add_custom_target commands. If you want to add file-level dependencies see the DEPENDS option of the add_custom_target and add_custom_command commands.
Signed-off-by: Alexey Shvetsov email@example.com