define equivalence class and partition of a relation code example

Example: equivalence class partitioning

Equivalence Partitioning is type of black box
testing technique which can be applied to
all levels of software testing like unit,
integration, system, etc. In this technique,
input data units are divided into equivalent
partitions that can be used to derive test
cases which reduces time required for testing 
because of small number of test cases.

It divides the input data of software
into different equivalence data classes.
You can apply this technique, 
where there is a range in the input field.