Why seems add_rostest not to work?

edit

I am migrating a packet to catkin. It contains a test. The test runs successfully like this:

rostest my_navigation_test my_test_4_cob.test

but when i add

add_rostest(launch/my_test_4_cob.test)

to the equivalent CMakeLists.txt and call catkin_make test I get:

catkin_make test
Base path: /home/aub-ch/ros/hydro_mynavigationtest
Source space: /home/aub-ch/ros/hydro_mynavigationtest/src
Build space: /home/aub-ch/ros/hydro_mynavigationtest/build
Devel space: /home/aub-ch/ros/hydro_mynavigationtest/devel
Install space: /home/aub-ch/ros/hydro_mynavigationtest/install
####
#### Running command: "make cmake_check_build_system" in "/home/aub-ch/ros/hydro_mynavigationtest/build"
####
####
#### Running command: "make test -j8 -l8" in "/home/aub-ch/ros/hydro_mynavigationtest/build"
####
Running tests...
Test project /home/aub-ch/ros/hydro_mynavigationtest/build
    Start 1: _ctest_my_navigation_test_rostest_launch_my_test_4_cob.test
1/1 Test #1: _ctest_my_navigation_test_rostest_launch_my_test_4_cob.test ...***Failed    5.64 sec

0% tests passed, 1 tests failed out of 1

Total Test time (real) =   5.66 sec

The following tests FAILED:
      1 - _ctest_my_navigation_test_rostest_launch_my_test_4_cob.test (Failed)
Errors while running CTest
make: *** [test] Error 8
Invoking "make" failed

It is a bit hard to debug as it gives no feedback about what is really happening at all.
Any ideas?

Can you explain to me what the line '_ctest_my_navigation_test_rostest_launch_my_test_4_cob.test' means? Does it expect the launchfile to be called like this? (which it isn't)