The tests have been converted with minimal changes (but this could be a bit
difficult to see without the "-w" diff option as there have been many changes
in indentation), basically we just use CATCH CHECK() (and REQUIRE(), in a few
places where it is appropriate) macro instead of assert() and the test driver
now just uses Catch::Session::run() instead of enumerating the tests to run
explicitly.

This has a lot of advantages such as:

- Provides information about the failed test and the values of variables in it.
- Allows to continue running the tests even if one of them fails.
- Allows to run just some of the tests with flexible selection mechanism.