[CMake] CTest with multiple directories: problem with absolute paths

[Tyler Roscoe]

Assume a project like this:

- top-level CMakeLists (calls add_subdirectory() on:)
    - unittest CMakeLists where add_test() is called on a bunch of
      unit tests in this directory
    - (there are many pockets of unit tests in different unittest
      directories.)

I want to be able to run ctest either from the unittest level, where it
will run just the unit tests in that directory; or from the top level,
where it will default to running all the unit tests in the system (but
where ctest may run a subset of all the unit tests as instructed by -R
or -E or -I).


Running at the unittest level already works.

To try to get it to work at the top level, the first thing I had to do
was enable_testing() in my top-level CMakeLists. Doing this caused CMake
to generate a CTestTestfile.cmake in my top-level binary directory.
CTestTestfile.cmake includes, among other things:

SUBDIRS(/path/to/unittest/_build/linux/debug)



Question 1: Why is CTestTestfile.cmake using the deprecated SUBDIRS()
command instead of add_subdirectory()?



Question 2: Why doesn't this work?

$ ctest
Start processing tests
Test project /path/to/toplevel/_build/linux/debug
No tests were found!!!


I have verified that all paths are correct and accessible.




Question 3: Why *does* it work if I switch to using relative paths
instead of absolute paths?

If I edit my CTestTestfile.cmake to instead use a relative path to that
same directory:

SUBDIRS(../../../../path/to/unittest/_build/linux/debug)

now it works great:

$ ctest
Start processing tests
Test project /path/to/toplevel/_build/linux/debug
  1/  7 Testing SomeTest                   Passed
  2/  7 Testing SomeTest                   Passed
  3/  7 Testing SomeTest                   Passed
  4/  7 Testing SomeTest                   Passed
  5/  7 Testing SomeTest                   Passed
  6/  7 Testing SomeTest                   Passed
  7/  7 Testing SomeTest                   Passed

100% tests passed, 0 tests failed out of 7



TIA,
tyler