Classification Tree Method - Easy solving

In Test Analyst course, we get to study about number of Test design techniques. In this post I am going to talk about one of those Test design techniques "Classification Tree Method". Tricks to easily solve the question in ISTQB exam by solving one of the sample question.

Classification Tree Method is one of the black box test design technique which is mainly used to test combinations of features.
Lets consider sample question from ISTQB Test Analyst syllabus

Q: Easytravel is a card which is used for paying journeys on buses and undergrounds. The user can
store credit to the card at the Easytravel Loading Machines and the system automatically deducts the
fee of the journey while the user shows the card to the card reader on a bus or at the underground
station. The system allows the user to load 10, 20, 30, 40, 50 Euros or another, user-defined amount to the card. There are four payment methods available: cash, credit card, debit card or pay-by-phone. After the transaction, the system allows the user to view or print the balance on a receipt
Using the Classification Tree method, what is the minimum number of test cases for 100 % 1-wise
coverage?

Answer:
A. 6 test cases
B. 2 test cases
C. 12 test cases
D. 3 test cases

Solution: 
In order to calculate the number of test cases, we need to identify the test relevant features called "Classifications" and their corresponding values called "Classes". By analyzing the requirement specification, we can identify classification and classes.

Considering the sample question above

Classification	No. of Classes	Details
Allowed amount loading	6	10, 20, 30, 40, 50 and user- defined amount
Payment methods	4	Cash, credit card, debit card and pay-by-phone
Show Balance	2	View and Print

In 1-wise coverage, each value of every parameter must be at least once included which is nothing but finding minimum number of test cases we get by applying classification tree method.

Now, let us find out the minimum and maximum number of test cases by applying Classification Tree Method.

Minimum number of test cases = Number of classes in the classification which has maximum number of classes 

Maximum number of test cases = Cartesian product of all classes.

Applying the formula in the above scenario to find out the minimum and maximum number of test cases.

Minimum number of test cases = 6 ( according to table above, classification which has max number of values is "allowed amount loading")
Maximum number of test cases = 48 (6 * 4 *2)

Answer: Option A. 6 Test Cases