Automatic generation of test data for a given path in a program is one of the elementary problems in software testing
the essence of which lies in the deriving and solving of system of constraints.The issue of how to solving nonlinear constraint is a hard problem in theory.In this paper
we classify the approaches of generation of test data for a given path into four categories:random
static
dynamic
and heuristic.The representative methods in each category are analyzed and compared.The direction of research is also explored.