ISTQB question: Statement Coverage and Decision Coverage with loop

Question

I'm learning ISTQB and encountering a question about Statement and Decision coverage in a sample exam of ISTQB org.

Evaluate the following control flow diagram and determine the statement coverage and decision coverage resulting from the execution of the following test cases:

• A-B-D-E-F
• A-B-C

There are 4 answer choice:

a. 33% statement, 100% decision

b. 50% statement, 50% decision

c. 100% statement, 75% decision

d. 100% statement, 100% decision

As the answer sheet, the correct one is: C. I understand why 100% statement , but 75% decision. We have 4 Test Cases:

1. A-B-C (test case 1)
2. A-B-D-E-F (test case 2)
3. A-B-D-A-B-C (test case 3)
4. A-B-D-A-B-D-E-F (test case 4)

So the coverage percentage is = the number of run test cases / the total of test cases = 2/4 = 50%. But it is not the same as the answer - 75%.

Am I understanding incorrectly?

Could you please help me point out what wrong it is and share more ideas on it?

Answer 1

You have 4 possible decisions/branches:

1. B-C
2. B-D
3. D-E
4. D-A

The 2 test cases A-B-D-E-F and A-B-C only cover 3 (1. – 3.) out of 4, which is why it's 75% decision/branch coverage.