Equivalence partitioning testing is a black box software testing technique in which input to the software or system is divided/partitioned into similar types of data so that they are likely to be behave similar way. One test data is picked from each group and if it passes, we assume that software will work for all the inputs of that group/class. if it fails, we assume that for all other value of that class, it will fails.
e.g. if any number field is of age and condition is of 18 to 56 valid inputs than by equivalence partitioning ,we can device input data in below class,
1. number <18 - invalid
2 18 >= number <= 56 - Valid
3. number greater than 56 - invalid
we can test for one value from each class and verify that condition for age field.