ISTQB: Easiest way to solve statement and branch coverage problems.

Several ISTQB aspirants face issues in answering the statement and branch coverage questions. These questions are really important to clear ISTQB certification.I got emails from several aspirants where they have asked me doubts on statements and branch coverage. So I decided to write this post.

Before learning how to solve these problem one needs to know the basics of  drawing flow chart.

Flowcharts use special shapes to represent different types of actions or steps in a process. Lines and arrows show the sequence of the steps, and the relationships among them. These are known as flowchart symbols.

Reference:https://www.smartdraw.com/flowchart/flowchart-symbols.htm

STATEMENT COVERAGE

You can say you have achieved 100% statement coverage if your test cases executes every statement in the code at-least once.

Let's solve a problem on statement coverage so that you know how to solve such question when asked in exam.

How many test case are required to achieve 100% statement coverage?

Switch PC on
Start "outlook"
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Tip: To achieve 100% statement coverage you need to execute all the statements (represented with rectangular boxes).You need to find out the shortest number of paths following which all the nodes will be covered. 

As you seen in diagram below in one path we can cover all statements. So 1 test case is enough to achieve 100% statement coverage.

If you are flying with an economy ticket, there is a possibility that you may get upgraded to business class, especially if you hold a gold card in the airline's frequent flier program. If you don't hold a gold card, there is a possibility that you will get 'bumped' off the flight if it is full and you check in late. This is shown in Figure 4.5.

Note that each box (i.e. statement) has been numbered. Three tests have been run:

Test 1: Gold card holder who gets upgraded to business class

Test 2: Non-gold card holder who stays in economy

Test 3: A person who is bumped from the flight

What is the statement coverage of these three tests?

a. 60%

b. 70%

c. 80%

d. 90%

The answer is 80%. There are 10 statements(boxes) and 8 have been covered by the tests run.

BRANCH/DECISION COVERAGE:

Branch coverage is also known as Decision coverage. It covers both the true and false conditions unlike statement coverage. We can say we have achieved 100% decision coverage if all the edges in the flow charts are covered by your test case.

How many test case are required to achieve 100% decision coverage?

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We need 2 test cases to achieve 100% decision coverage. 2 paths will ensure covering of all the edges as shown is figure below:

How many test cases are required for 100% decision coverage?

Read P
Read Q
IF P+Q > 100 THEN
Print “Large”
ENDIF
If P > 50 THEN
Print “P Large”
ENDIF

With 2 paths we can cover all the edges. So 2 test cases are required for 100% decision coverage.

Tips

• Cover all nodes for 100% statement coverage. 

• Cover all edges for 100% decision coverage.

You are often asked minimum number of test cases required to cover 100%statement and branch coverage in ISTQB exams.

PATH COVERAGE:

To achieve 100% path Coverage you need to cover all the paths from start to end. As far as I know you wont get questions to calculate path coverage in ISTQB certification exam.

How many test cases are required for 100% path coverage?

Read P
Read Q
IF P+Q > 100 THEN
Print “Large”
ENDIF
If P > 50 THEN
Print “P Large”
ENDIF

As shown in the illustration above, 4 test cases are required for 100% path coverage.

1A-2B-E-4F
1A-2B-E-4G-5H
1A-2C-3D-E-4G-5H
1A-2C-3D-E-4F

Remember

1. Branch coverage and Decision coverages are one and the same
2. 100% LCSAJ(Linear Code Sequence and Jump.) coverage implies 100% Branch/Decision coverage
3. 100% Path coverage implies 100% Statement coverage
4. 100% Branch/Decision coverage implies 100% Statement coverage
5. 100% Path coverage implies 100% Branch/Decision coverage

I have tried to explain the statement and decision coverage with simple techniques. I hope it helps!

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