Boundary Value Analysis(BVA): The concept behind this is to 
partition program domain in a meaningful way to generate 
data sets that span the partition are determined. This 
creates test cases around the boundaries of the valid data.
The values that can be passed are exact boundary values, +/-
 lowest boundary value and +/- highest boundary value

Consider a text box which can take a maximum of 255 
characters. Then the domain that can be considered is from 
1 to 255. The values that can be passed into the text box 
for testing would be 1, 255, 0,2,254 and 256.

Equalence Partitioning: This is to partition set of all 
possible inputs into classes that receive equivalent 
treatment. 

If consider the same example, the equivalence classes would 
be:

Class1: Values from 1 to 255, 1 and 255 inclusive
Class2: Values less than 1
Class3: Values more than 255

Error Guessing: This technique is used to find defects 
using the experience of the tester. Consider the above 
example, the textox is intended for characters only. The 
tester can easily give numbers or any special characters 
for that text box and see whether the application is 
throwing an exception or not.

The following are the error guessing techniques:
BVA(Boundary Value Analysis) is used for range values.
ECP(Equivalent Class Partition) is used for both range and 
non-range values.