We develop a new notion called {\it tester of a class $\cM$ of
functions} $f:\cA\to \cC$ that maps the elements $\bfa\in \cA$ in
the domain $\cA$ of the function to a finite number (the size of
the tester) of elements $\bfb_1,\ldots,\bfb_t$ in a smaller
sub-domain $\cB\subset \cA$ where the property ... more >>>