Wiktionary
n. The act of checking that something does not contain elementary mistakes or impossibility, or is not based on invalid assumptions
Wikipedia
A sanity test or sanity check is a basic test to quickly evaluate whether a claim or the result of a calculation can possibly be true. It is a simple check to see if the produced material is rational (that the material's creator was thinking rationally, applying sanity). The point of a sanity test is to rule out certain classes of obviously false results, not to catch every possible error. A rule-of-thumb may be checked to perform the test. The advantage of a sanity test, over performing a complete or rigorous test, is speed.
In arithmetic, for example, when multiplying by 9, using the divisibility rule for 9 to verify that the sum of digits of the result is divisible by 9 is a sanity test—it will not catch every multiplication error, however it's a quick and simple method to discover many possible errors.
In computer science, a sanity test is a very brief run-through of the functionality of a computer program, system, calculation, or other analysis, to assure that part of the system or methodology works roughly as expected. This is often prior to a more exhaustive round of testing.
Usage examples of "sanity check".
You are our best sanity check when it comes to questions about humankind.
As a final sanity check, a Landing Signals Officer--LSO--was stationed on a small platform that jutted out from the side of the carrier just below the level of the flight deck.
Calm, logical, and understanding, she provided Celine's sanity check for the next forty-eight hours.