How many test cases are needed to achieve 100 per cent decision coverage?

Consider the following pseudo code:

1 Begin

2 Read Time

3 If Time < 12 Then

4 Print(Time, "am")

5 Endif

6 If Time > 12 Then

7 Print(Time 12, "pm")

8 Endif

9 If Time = 12 Then

10 Print (Time, "noon")

11 Endif

12 End

How many test cases are needed to achieve 100 per cent decision coverage?
A . 1
B . 2
C . 3
D . 4

Answer: C

Explanation:

The three decisions are in sequence and the conditions are all mutually exclusive (if any one is true the others must be false). Hence a test case that makes the first decision true will make the second and third decisions false and so on.

So test case 1 (say Time = 6) would exercise the path True, False, False, test case 2 (say Time = 15) would exercise the path False, True, False. Test case 3 would have to be Time = 12. This combination achieves 100 per cent decision coverage because each decision has been exercised through its true and its false outcomes.