from the comments of http://bugs.musicbrainz.org/ticket/3778

cmake has the ability to build outside the source tree. (Which should be used, whenever possible, in my opinion.) So if I have the source code in source, I could do:
mkdir build && cd build
cmake ../source -DFoo...
make
make check

With an in-source build I would do (and I guess, that it what you do):
cd source
cmake . -DFoo...
make
make check

Now, the first works, the second doesn't. It builds fine in both cases, but fails to run the tests in the first. Hope that clears it up a but.