17. You are testing a PIN validator, which accepts valid PINs and rejects invalid PINs. A PIN is a sequence of digits. A PIN is valid if it consists of four digits, at least two of which are different. You have identified the following valid equivalence partitions:
Variable: PIN code length
• The partition “length correct” - four-digit PINs
• The partition “length incorrect” - PINs with length other than 4
Variable: Number of different digits
• The partition “number of different digits correct” - PINs with at least two different digits
• The partition “number of different digits incorrect” - PINs with all digits being the same
Which of the following is a MINIMUM set of input test data that covers all identified equivalence partitions?
Explanation / Rationale
a) Is correct. Value “1” covers “length incorrect” and covers “number of different digits incorrect”, however the system would not validate against this partition when hitting the first incorrect partition. Value “1111” covers “length correct” and “number of different digits incorrect. Value “1234” again covers “length correct” and also “number of different digits correct”
b) Is not correct. These three values achieve full coverage of the equivalence partitions, but full coverage can be achieved with two values
c) Is not correct. These two values only cover “number of different digits
d) Is not correct. These two values does not cover “number of different digits incorrect” equivalence partition