[CMake] directory traverse guidance

[luxInteg]

Greetings

I am learning cmake

consider my project  with  two directories  dir1 and dir2 

if I want to:-
move to dir1 and  add a library libA  in dir1  
move to dir2 and  add a library libB  in dir2 
move back to dir1 and add a test  testA in dir1
move back to dir2 and add a test  testB to dir2


(the moving back is because of  the  interdependencies  of the tests with the 
libraries  i.e.       testA reaquires libB etc))

how do I do this?

sincerely
luxInteg