Java Custom Assertion Example: Providing Meaningful feedback in tests

Java Unit Test: Exercise-7 with Solution

Write a Java program that uses assertions with custom error messages to provide meaningful feedback when a test fails.

Sample Solution:

Java Code:

// CustomAssertionTest.java

import org.junit.Test;
import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

public class CustomAssertionTest {

    public void testAddition() {
        int result = add(2, 3);
        assertWithMessage("Addition failed: ", result == 5);

    public void testMultiplication() {
        int result = multiply(2, 3);
        assertWithMessage("Multiplication failed: ", result == 6);

    private int add(int a, int b) {
        return a + b;

    private int multiply(int a, int b) {
        return a * b;

    private static void assertWithMessage(String message, boolean condition) {
        assert condition : message;

    public static void main(String[] args) {
        Result result = JUnitCore.runClasses(CustomAssertionTest.class);

        // Check if there are any failures
        if (result.getFailureCount() > 0) {
            System.out.println("Test failed:");

            // Print details of failures
            for (Failure failure : result.getFailures()) {
        } else {
            System.out.println("All tests passed successfully.");

Sample Output:

All tests passed successfully.


In the exercise above-

  • assertWithMessage Method: This method takes a custom error message and a boolean condition. It uses the "assert" statement to check the condition, and if the condition is false, it throws an "AssertionError" with the provided custom message.
  • testAddition and testMultiplication Methods: These are JUnit test methods that use custom assertions with meaningful error messages.
  • main Method: Runs the JUnit tests and prints whether the tests passed or failed. If a test fails, it prints details about the failures.
  • add and multiply Methods: These are example methods that perform addition and multiplication, respectively.

When running this program, if a test fails, the custom error message specified in the "assertWithMessage" method will provide additional context about the failure.


Flowchart: Java Custom Assertion Example: Providing Meaningful feedback in tests
Flowchart: Java Custom Assertion Example: Providing Meaningful feedback in tests

Java Code Editor:

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