There are 5 types of black box testing techniques.

First one is equivalent class partitioning.Lets understand with an example

If there is a input field accepting a number between 20 to 50 So we divide values into three equivalent classes

1. age <20(invalid partition)

2. 20<=age<=50(valid partition)

3. 3.age>50(invalid partition)

So we deal with a smaller sub set that represents the entire bigger subset.

So every subset of data we choose from a bigger subset is a representative of bigger subset and we can say if the test passes for the smaller subset it will pass for bigger subset.In this way we don’t have to test each and every combination of data.

Another example –

If an input field accepts any number between 1-1000 So for valid values we chose 4 tests -

1. One digit numbers like anything from 1-9
2. Two digit numbers like 10-99
3. Three digit numbers like 100-999
4. And 4 digit numbers like 1000 itself.

We also check at the boundaries in this case Like LB-1 ,LB ,LB+1 And UB-1 ,UB ,UB+1 Where LB is lower boundary i.e 1 And UB is upper boundary i.e 1000.

Any value present in any of these three classes is equivalent to value present in any other value in that class hence the name equivalent partitioning