Code Coverage Tool: Statement, Branch & Decision Testing

What is Code Coverage?

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

In most cases, a code coverage system gathers information about the running program. It then 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 measure the efficiency of test implementation.
• It offers a quantitative measurement of testing.
• It defines the degree to which the source code has been tested.

Code Coverage Methods

The following are the 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 to calculate the number of statements in the source code that have been executed. The main purpose of Statement Coverage is to cover all the possible paths, lines, and statements in the source code.

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

In white box testing, the tester concentrates on how the software works. In other words, the tester concentrates on the internal working of the source code concerning control flow graphs or flow charts.

Generally in any software, if you look at the source code, there will be a wide variety of elements like operators, functions, looping, exception handlers, and so on. 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 paths, lines, and statements in the code.

Let us understand this with an example of how to calculate statement coverage. Here we take 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: If A = 3, B = 9

The statements marked in yellow are those which are executed as per the scenario. Number of executed statements = 5, Total number of statements = 7, so Statement Coverage = 5/7 = 71%.

Scenario 2: If A = -3, B = -9

The statements marked in yellow are those which are executed as per the scenario. Number of executed statements = 6, Total number of statements = 7, so Statement Coverage = 6/7 = 85%.

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

What is covered by Statement Coverage?

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

Decision Coverage Testing

Decision Coverage is a white box testing technique which reports the true or false outcomes of each boolean expression in 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 type, expressions can become complex, making it challenging to achieve 100% coverage. This is why various methods are used to report this metric. These methods prioritize the most critical combinations. While it is similar to branch coverage, it provides greater 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 “No” outcome of the decision If (a>5) is checked, so Decision Coverage = 50%.

Scenario 2: Value of a is 6. The “Yes” outcome of the decision If (a>5) is checked, so 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 measure fractions of independent code segments and find out sections that have 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, consider the same example used earlier. Branch Coverage will consider the unconditional branch as well.

Advantages of Branch coverage:

• Allows you to validate all the branches in the code.
• Helps you ensure that no branch leads to any abnormality in the program’s operation.
• Removes issues that happen because of statement coverage testing.
• Allows you to find areas which are not tested by other testing methods.
• Allows you to find a quantitative measure of code coverage.
• Branch coverage ignores branches inside 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 a 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, only expressions with logical operands are considered.

For example, if an expression has boolean operations like AND, OR, or XOR, that indicates the total possibilities. Condition coverage does not guarantee full decision coverage.

The formula to calculate Condition Coverage:

For an expression with two operands, there are four possible combinations: TT, FF, TF, and FT. Consider the input X=3, Y=4 (x<y) TRUE and A=3, B=4 (a>b) FALSE, which gives Condition Coverage of 1/4 = 25%.

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 at how many times specific states are visited or 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 whether the:

• code under test has single or multiple undiscovered defects,
• cost of the potential penalty,
• cost of lost reputation,
• cost of lost sales, and so on.

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

FAQs