Include files are often used in the mtr to perform environment checks and skip the test where it's not applicable.

The problem is — if the file is included in many tests, it'll be run as many times, as a part of the test. And running the test is not cheap.

We may want to let mtr to cache the result of the check. Say, it remembers that not_windows.inc failed once and automatically skips all other tests that include this file.

Unsolved question — what to do with the include files that may behave differently in different test files?