Block box testing techniques

The main difference between EP and BVA is that EP determines the number of test cases to be generated for a given scenario where as BVA will determine the effectiveness of those generated test cases.

Equivalence partitioning : Equivalence Partitioning determines the number of test cases for a given scenario.
Equivalence partitioning is a black box testing technique with the following goal:
1.To reduce the number of test cases to a necessary minimum.
2.To select the right test cases to cover all possible scenarios.

Here we are dividing input values to be given into valid and invalid values

It is a Black Box Testing Technique that divides the input domain into classes of data from which test cases can be derived.

BVA
This is also a Black Box Testing Technique which concentrates on the Corner cases or the boundaries of the input domain rather than its center

Exapmle
username: min length=4
max length=7
alphanumeric
for this if u where to write BVA and ECP
then it is in this manner
BVA
min+1 valid
min-1 invalid
max+1 invalid
max-1 valid
ECP
valid Invalid
0-9 special characters
a-z

Error Guessing:-
Error Guessing comes with experience with the technology and the project. Error Guessing is the art of guessing where errors can be hidden. There are no specific tools and techniques for this, but you can write test cases depending on the situation: Either when reading the functional documents or when you are testing and find an error that you have not documented.