[CMake] Something like CTEST_CUSTOM_PRE_TEST, but for individual projects?

[Dan Kegel]

I'm porting a large project with many subdirectories from autotools to
cmake and ctest.
It's going well, but I ran into a question on how to do test setup/teardown.
I've got CTEST_CUSTOM_PRE_TEST working nicely, but now I need different
conditions for each directory's worth of tests.  Is there anything like
CTEST_CUSTOM_PRE_TEST that gets run at the beginning of each subprojects'
tests?