Pragmatic Unit Testing in Java 8 with JUnit

Right-BI[C]EP: Cross-Checking Using Other Means

Any interesting problem has umpteen solutions. You choose a blue-ribbon winner, perhaps because it performs or smells better. That leaves the “loser” solutions available for cross-checking the production results. Maybe the runners-up are too slow or inflexible for production use, but they can help cross-check your winning choice, particularly if they’re trusted ‘n’ true.

We can use the “inferior” Java library implementation of square root to cross-check. (Apparently we suffer from bad egos.) We check whether or not our new superspiffy square-root logic produces the same results as Math.sqrt():