Source : Free On-Line Dictionary of Computing

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)