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What is Equivalence partitioning?
Equivalence partitioning is a method for deriving test cases. In this method, equivalence classes (for input values) are identified such that each member of the class causes the same kind of processing and output to occur. The values at the extremes (start/end values or lower/upper end values) of such class are known as Boundary values. Analyzing the behavior of a system using such values is called Boundary value analysis(BVA).
Here are few sample questions for practice from ISTQB exam papers on Equivalence partitioning and BVA. (Ordered: Simple to little complex)

Question 1
One of the fields on a form contains a text box which accepts numeric values in the range of 18 to 25. Identify the invalid Equivalence class.
a)    17
b)    19
c)    24
d)    21
Solution
The text box accepts numeric values in the range 18 to 25 (18 and 25 are also part of the class). So this class becomes our valid class. But the question is to identify invalid equivalence class. The classes will be as follows:
Class I: values < 18   => invalid class
Class II: 18 to 25       => valid class
Class III: values > 25 => invalid class
17 fall under invalid class. 19, 24 and 21 fall under valid class. So answer is ‘A’
Question 2
In an Examination a candidate has to score minimum of 24 marks in order to clear the exam. The maximum that he can score is 40 marks.  Identify the Valid Equivalence values if the student clears the exam.
a)    22,23,26
b)    21,39,40
c)    29,30,31
d)    0,15,22
Solution
The classes will be as follows:
Class I: values < 24   => invalid class
Class II: 24 to 40       => valid class
Class III: values > 40 => invalid class
We have to indentify Valid Equivalence values. Valid Equivalence values will be there in Valid Equivalence class. All the values should be in Class II. So answer is ‘C’
Question 3
One of the fields on a form contains a text box which accepts alpha numeric values. Identify the Valid Equivalence class
a)    BOOK
b)    Book
c)    Boo01k
d)    Book
Solution
Alpha numeric is combination of alphabets and numbers. Hence we have to choose an option which has both of these. A valid equivalence class will consist of both alphabets and numbers. Option ‘c’ contains both alphabets and numbers. So answer is ‘C’
Question 4
The Switch is switched off once the temperature falls below 18 and then it is turned on when the temperature is more than 21. When the temperature is more than 21. Identify the Equivalence values which belong to the same class.
a)    12,16,22
b)    24,27,17
c)    22,23,24
d)    14,15,19
Solution
We have to choose values from same class (it can be valid or invalid class). The classes will be as follows:
Class I: less than 18 (switch turned off)
Class II: 18 to 21
Class III: above 21 (switch turned on)
Only in Option ‘c’ all values are from one class. Hence the answer is ‘C’. (Please note that the question does not talk about valid or invalid classes. It is only about values in same class)
Question 5
A program validates a numeric field as follows: values less than 10 are rejected, values between 10 and 21 are accepted, values greater than or equal to 22 are rejected. Which of the following input values cover all of the equivalence partitions?
a. 10,11,21
b. 3,20,21
c. 3,10,22
d. 10,21,22
Solution
We have to select values which fall in all the equivalence class (valid and invalid both). The classes will be as follows:
Class I: values <= 9   => invalid class
Class II: 10 to 21       => valid class
Class III: values >= 22 => invalid class
All the values from option ‘c’ fall under all different equivalence class. So answer is ‘C’.
Question 6
A program validates a numeric field as follows: values less than 10 are rejected, values between 10 and 21 are accepted, values greater than or equal to 22 are rejected. Which of the following covers the MOST boundary values?
a. 9,10,11,22
b. 9,10,21,22
c. 10,11,21,22
d. 10,11,20,21
Solution
We have already come up with the classes as shown in question 5. The boundaries can be identified as 9, 10, 21, and 22. These four values are in option ‘b’. So answer is ‘B’
Question 7
In a system designed to work out the tax to be paid:
An employee has £4000 of salary tax free.
The next £1500 is taxed at 10%.
The next £28000 after that is taxed at 22%.
Any further amount is taxed at 40%.
To the nearest whole pound, which of these groups of numbers fall into three DIFFERENT equivalence classes?
a)    £4000; £5000; £5500
b)    £32001; £34000; £36500
c)    £28000; £28001; £32001
d)    £4000; £4200; £5600
Solution
The classes will be as follows:
Class I   : 0 to £4000          => no tax
Class II  : £4001 to £5500   => 10 % tax
Class III : £5501 to £33500 => 22 % tax
Class IV : £33501 and above => 40 % tax
Select the values which fall in three different equivalence classes. Option ‘d’ has values from three different equivalence classes. So answer is ‘D’.
Question 8
In a system designed to work out the tax to be paid:
An employee has £4000 of salary tax free.
The next £1500 is taxed at 10%.
The next £28000 after that is taxed at 22%.
Any further amount is taxed at 40%.
To the nearest whole pound, which of these is a valid Boundary Value Analysis test case?
a)    £28000
b)    £33501
c)    £32001
d)    £1500
Solution
The classes are already divided in question # 7. We have to select a value which is a boundary value (start/end value). 33501 is a boundary value. So answer is ‘C’.
Question 9
Given the following specification, which of the following values for age are in the SAME equivalence partition?
If you are less than 18, you are too young to be insured.
Between 18 and 30 inclusive, you will receive a 20% discount.
Anyone over 30 is not eligible for a discount.
a)    17, 18, 19
b)    29, 30, 31
c)    18, 29, 30
d)    17, 29, 31
Solution
The classes will be as follows:
Class I: age < 18       => not insured
Class II: age 18 to 30 => 20 % discount
Class III: age > 30     => no discount
Here we cannot determine if the above classes are valid or invalid, as nothing is mentioned in the question. (But according to our guess we can say I and II are valid and III is invalid. But this is not required here.) We have to select values which are in SAME equivalence partition. Values from option ‘c’ fall in same partition. So answer is ‘C’.
These are few sample questions for practice from ISTQB papers. We will continue to add more ISTQB question papers with answers in coming posts.