[CMake] ctest: how to skip tests?

[Dave Milter]

Hi.

I have project with usage of cmake and ctest.

Now I need to add tests, that may have sense or not have sense to run
on certain machine.

For example, if we have installed MySql and libmysql there is sense to
test part of code working with mysql, but no sense to check parts that
working with
postgresql or oracle, if there are no such software on machine.

But all code that work with different databases are part of our product,
so we need to warn that some part of test suite is not running.

In several test suites, for example suite to write Python unit tests,
there is ability to
mark test as SKIPPED, so there are not two states, PASSED and NOT PASSED,
but also SKIPPED,

so if you would be me, what and how you modify in ctest code to make
this possible?