Enable out-of-source builds

The only thing preventing this was the tests requiring access to some files to run
The simple fix for now is to have the tests run in that directory.
There might be a better fix option but this will do for now.

Author: saxbophone

CMakeLists.txt

@@ -122,7 +122,7 @@ enable_testing()
 include(CTest)
 include(Catch)
 
-catch_discover_tests(unit_tests)
+catch_discover_tests(unit_tests WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}/tests")
 
 install(
     TARGETS dengr