Code Coverage Tutorial: Branch, Statement & Decision Testing

Code coverage is a measure which describes the degree of which the source code of the program has been tested. It is one form of white box testing which finds the areas of the program not exercised by a set of test cases. It also creates some test cases to increase coverage and determining a quantitative measure of code coverage.

In most cases, code coverage system gathers information about the running program. It also combines that with source code information to generate a report about the test suite’s code coverage.

Why use Code Coverage Testing?

Here, are some prime reasons for using code coverage:

• It helps you to measure the efficiency of test implementation
• It offers a quantitative measurement.
• It defines the degree to which the source code has been tested.

Code Coverage Methods

Following are major code coverage methods

• Statement Coverage
• Decision Coverage
• Branch Coverage
• Toggle Coverage
• FSM Coverage

Statement Coverage

Statement Coverage is a white box testing technique in which all the executable statements in the source code are executed at least once. It is used for calculation of the number of statements in source code which have been executed. The main purpose of Statement Coverage is to cover all the possible paths, lines and statements in source code.

Statement coverage is used to derive scenario based upon the structure of the code under test.

In White Box Testing, the tester is concentrating on how the software works. In other words, the tester will be concentrating on the internal working of source code concerning control flow graphs or flow charts.

Generally in any software, if we look at the source code, there will be a wide variety of elements like operators, functions, looping, exceptional handlers, etc. Based on the input to the program, some of the code statements may not be executed. The goal of Statement coverage is to cover all the possible path’s, line, and statement in the code.

Let’s understand this with an example, how to calculate statement coverage.

Scenario to calculate Statement Coverage for given source code. Here we are taking two different scenarios to check the percentage of statement coverage for each scenario.

Source Code:

Prints (int a, int b) < ------------ Printsum is a function int result = a+ b; If (result>0) Print ("Positive", result) Else Print ("Negative", result) > ----------- End of the source code

Scenario 1:

The statements marked in yellow color are those which are executed as per the scenario

Number of executed statements = 5, Total number of statements = 7

Statement Coverage: 5/7 = 71%

Likewise we will see scenario 2,

Scenario 2:

The statements marked in yellow color are those which are executed as per the scenario.

Number of executed statements = 6

Total number of statements = 7

Statement Coverage: 6/7 = 85%

But overall if you see, all the statements are being covered by both scenarios. So we can conclude that overall statement coverage is 100%.

What is covered by Statement Coverage?

1. Unused Statements
2. Dead Code
3. Unused Branches
4. Missing Statements

RELATED ARTICLES

• What is Software Testing?
• 7 Principles of Software Testing with Examples

Decision Coverage Testing

Decision Coverage is a white box testing technique which reports the true or false outcomes of each boolean expression of the source code. The goal of decision coverage testing is to cover and validate all the accessible source code by checking and ensuring that each branch of every possible decision point is executed at least once.

In this coverage, expressions can sometimes get complicated. Therefore, it is very hard to achieve 100% coverage. That’s why there are many different methods of reporting this metric. All these methods focus on covering the most important combinations. It is very much similar to decision coverage, but it offers better sensitivity to control flow.

Example of decision coverage

Consider the following code-

Demo(int a) < If (a>5) a=a*3 Print (a) >

Scenario 1:

Value of a is 2

The code highlighted in yellow will be executed. Here the “No” outcome of the decision If (a>5) is checked.

Decision Coverage = 50%

Scenario 2:

Value of a is 6

The code highlighted in yellow will be executed. Here the “Yes” outcome of the decision If (a>5) is checked.

Decision Coverage = 50%

Branch Coverage Testing

Branch Coverage is a white box testing method in which every outcome from a code module(statement or loop) is tested. The purpose of branch coverage is to ensure that each decision condition from every branch is executed at least once. It helps to measure fractions of independent code segments and to find out sections having no branches.

For example, if the outcomes are binary, you need to test both True and False outcomes.

The formula to calculate Branch Coverage:

Example of Branch Coverage

To learn branch coverage, let’s consider the same example used earlier

Consider the following code-

Demo(int a) < If (a>5) a=a*3 Print (a) >

Branch Coverage will consider unconditional branch as well

Advantages of Branch coverage:

Branch coverage Testing offers the following advantages:

• Allows you to validate-all the branches in the code
• Helps you to ensure that no branched lead to any abnormality of the program’s operation
• Branch coverage method removes issues which happen because of statement coverage testing
• Allows you to find those areas which are not tested by other testing methods
• It allows you to find a quantitative measure of code coverage
• Branch coverage ignores branches inside the Boolean expressions

Condition Coverage Testing

Condition Coverage or expression coverage is a testing method used to test and evaluate the variables or sub-expressions in the conditional statement. The goal of condition coverage is to check individual outcomes for each logical condition. Condition coverage offers better sensitivity to the control flow than decision coverage. In this coverage, expressions with logical operands are only considered.

For example, if an expression has Boolean operations like AND, OR, XOR, which indicates total possibilities.

Condition coverage does not give a guarantee about full decision coverage.

The formula to calculate Condition Coverage:

Example:

For the above expression, we have 4 possible combinations

Consider the following input

Finite State Machine Coverage

Finite state machine coverage is certainly the most complex type of code coverage method. This is because it works on the behavior of the design. In this coverage method, you need to look for how many time-specific states are visited, transited. It also checks how many sequences are included in a finite state machine.

Which Type of Code Coverage to Choose

This is certainly the most difficult answer to give. In order to select a coverage method, the tester needs to check that the

• code under test has single or multiple undiscovered defects
• cost of the potential penalty
• cost of lost reputation
• cost of lost sale, etc.

The higher the probability that defects will cause costly production failures, the more severe the level of coverage you need to choose.

Code Coverage vs. Functional Coverage

Code Coverage Tools

Here, is a list of Important code coverage Tools:

Advantages and Disadvantages of Using Code Coverage

Summary

• Code coverage is a measure which describes the degree of which the source code of the program has been tested
• It helps you to measure the efficiency of test implementation
• Five Code Coverage methods are 1.) Statement Coverage 2.) Condition Coverage 3) Branch Coverage 4) Toggle Coverage 5) FSM Coverage
• Statement coverage involves execution of all the executable statements in the source code at least once
• Decision coverage reports the true or false outcomes of each Boolean expression
• In the branch coverage, every outcome from a code module is tested
• Conditional will reveal how the variables or subexpressions in the conditional statement are evaluated
• Finite state machine coverage is certainly the most complex type of code coverage method
• In order to select a coverage method, the tester needs to check the cost of the potential penalty, lost reputation, lost sale, etc.
• Code coverage tells you how well the source code has been exercised by your test bench while Functional coverage measures how well the functionality of the design has been covered
• Cobertura, JTest, Clover, Emma, Kalistick are few important code coverage tools
• Code Coverage allows you to create extra test cases to increase coverage
• Code Coverage does not help you to determine whether we tested all possible values of a feature

You Might Like: