Equivalence partitioning is a method for deriving test cases. In this
method, classes of input conditions called equivalence classes are
identified such that each member of the class causes the same kind of
processing and output to occur.
In this method, the tester identifies various equivalence classes for partitioning. A class
is a set of input conditions that are is likely to be handled the same way
by the system. If the system were to handle one case in the class
erroneously, it would handle all cases erroneously.