Boundary value testing

is a technique to find whether the application is accepting the expected range of values and rejecting the values which falls out of range.
Ex. A user ID text box has to accept alphabet characters ( a-z ) with length of 4 to 10 characters.
BVA is done like this, max value:10 pass; max-1: 9 pass;
max+1=11 fail ;min=4 pass;min+1=5 pass;min-1=3 fail;
Like wise we check the corner values and come out with a conclusion whether the application is accepting correct range of values.