add `run-tests` which runs arbitrary number of tests
add `run-tests` which runs arbitrary number of tests

There was only one function `run-all-tests` which runs all the tests
at once.
To provide more convenient ways to run tests, `run-tests` is added.
It takes list of tests and run them, so you can add functions choose
tests to run and run them by just passing them to `run-tests` easily.

NobuoK/xyzzy,NobuoK/xyzzy,NobuoK/xyzzy,NobuoK/xyzzy,NobuoK/xyzzy