Why coverage measures test completeness in JUnit - Test Execution Impact

Test Overview

This test checks if all methods in a simple Calculator class are called during testing. It verifies test completeness by measuring code coverage.

Test Code - JUnit 5

JUnit

import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;

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

public class CalculatorTest {
    @Test
    void testAdd() {
        Calculator calc = new Calculator();
        int result = calc.add(5, 3);
        assertEquals(8, result);
    }
}

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initializes	-	PASS
2	CalculatorTest.testAdd() method is called	Calculator instance created	-	PASS
3	Calculator.add(5, 3) method is called	Inside add method, parameters a=5, b=3	-	PASS
4	add method returns 8	Return value 8 passed back to testAdd	-	PASS
5	testAdd asserts result equals 8	Assertion compares expected 8 with actual 8	assertEquals(8, result)	PASS
6	Test ends	Test runner completes testAdd	-	PASS
7	Coverage report generated	Report shows add method covered, subtract method not covered	Coverage measures which methods ran during tests	PASS

Failure Scenario

Failing Condition: If the add method is not called in any test

Execution Trace Quiz - 3 Questions

What does code coverage measure in this test?

A The number of assertions in the test

B How fast the test runs

C Which methods were executed during testing

D The memory used by the test

Key Result

Measuring code coverage helps ensure tests run all important parts of the code, showing test completeness.