The Jargon File (version 4.4.7, 29 Dec 2003):

sanity check
 n.

    [very common]

    1. The act of checking a piece of code (or anything else, e.g., a Usenet
    posting) for completely stupid mistakes. Implies that the check is to make
    sure the author was sane when it was written; e.g., if a piece of
    scientific software relied on a particular formula and was giving
    unexpected results, one might first look at the nesting of parentheses or
    the coding of the formula, as a sanity check, before looking at the more
    complex I/O or data structure manipulation routines, much less the
    algorithm itself. Compare reality check.

    2. A run-time test, either validating input or ensuring that the program
    hasn't screwed up internally (producing an inconsistent value or state).

    3. Conversationally, saying ?sanity check? means you are requesting a check
    of your assumptions. ?Wait a minute, sanity check, are we talking about the
    same Kevin here??


The Free On-line Dictionary of Computing (30 December 2018):

sanity check

    1. Checking code (or anything else, e.g. a
   Usenet posting) for completely stupid mistakes.  Implies
   that the check is to make sure the author was sane when it was
   written; e.g. if a piece of scientific software relied on a
   particular formula and was giving unexpected results, one
   might first look at the nesting of parentheses or the coding
   of the formula, as a "sanity check", before looking at the
   more complex I/O or data structure manipulation routines, much
   less the algorithm itself.

   Compare reality check.

   2. A run-time test, either validating input or ensuring that
   the program hasn't screwed up internally (producing an
   inconsistent value or state).

   [Jargon File]

   (1998-08-29)