Test Coverage Tutorial

What is Test Coverage?

Test coverage is a measure used to describe the degree to which the source code of a program is tested by a particular test suite. It helps determine how much of the code has been exercised by tests, ensuring that the software behaves as expected in various scenarios.

Importance of Test Coverage

Test coverage is crucial for several reasons:

• It helps identify untested parts of a codebase.
• Higher coverage often correlates with fewer bugs in production.
• It can improve the design of the code by encouraging modularity.
• It aids in maintaining code quality over time.

Types of Test Coverage

There are several types of test coverage metrics, including:

• Line Coverage: Measures the percentage of lines executed during tests.
• Branch Coverage: Measures the percentage of branches (if statements, loops) executed.
• Function Coverage: Measures whether each function in the program has been called.
• Statement Coverage: Measures the percentage of executable statements executed during tests.

How to Measure Test Coverage in Eclipse

Eclipse provides built-in tools to measure test coverage. Here’s how you can do it:

1. Install the EclEmma plugin for Eclipse.
2. Write your unit tests using JUnit.
3. Run your tests with coverage:

Right-click on your test class in the Project Explorer and select:

Coverage As > JUnit Test
4. View the coverage report generated by EclEmma.

Example of Test Coverage

Let’s look at a simple Java example to illustrate test coverage:

public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }

    public int subtract(int a, int b) {
        return a - b;
    }
}
                    

import org.junit.Test;
import static org.junit.Assert.*;

public class CalculatorTest {
    Calculator calculator = new Calculator();

    @Test
    public void testAdd() {
        assertEquals(5, calculator.add(2, 3));
    }

    // No test for subtract method
}
                    

Best Practices for Achieving Good Test Coverage

Here are some best practices to follow:

• Aim for at least 80% code coverage, but don't rely solely on the percentage.
• Write tests for edge cases and error handling.
• Use code reviews to ensure tests cover critical paths.
• Regularly review and update tests as the code evolves.

Conclusion

Test coverage is an essential aspect of software testing that helps ensure that your code is reliable and maintainable. By understanding and measuring test coverage, developers can identify untested code, reduce bugs, and improve overall code quality.