Use Test::Unit::TestCase for testing assert_value so that tests pass in all ruby versions without changes
Failproof support for various testing framework combinations.
Make sure we support:
1) test/unit from Ruby 1.8
2) old minitest 2.x-4.x, either bundled with Ruby 1.9 - 2.1 or installed via gem
3) new minitest 5.x from minitest gem (required for example by Rails 4.1)

Also, disable command line option parsing for minitest <5x when used with 'minitest/autorun'.
That combination is not supported yet. Minitest <5x with 'test/unit' is fine.
Properly increment assertion counts in all supported test suites