it "should raise an error for string with illegal characters" do
  Test.expect_error(luck_check('6F43E8'))
end 

is obviously wrong - can't catch an exception that has already happened. that needs to be in a block. still strange that it doesn't complain when it doesn't raise when that's what it says it tests for. doesn't really matter though, unless this also happens for MRI 3.0.0