how to test comparator code example

Example: what are test comparators

Is it really a test if you put some 
inputs into some software, but never
look to see whether the software produces the
correct result?
• The essence of testing is to check
whether the software produces the
correct result, and to do that, we must compare
what the software produces to what it should produce.
• A test comparator helps to automate 
aspects of that comparison.