Java Custom Assertion Example: Providing Meaningful feedback in tests

Last update on May 23 2025 13:13:41 (UTC/GMT +8 hours)

7. Assert with Custom Error Message

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 {

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

    @Test
    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()) {
                System.out.println(failure.toString());
            }
        } else {
            System.out.println("All tests passed successfully.");
        }
    }
}

Sample Output:

All tests passed successfully.

Explanation:

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:

For more Practice: Solve these Related Problems:

Write a Java program to create a test case using assertEquals with a custom error message for detailed failure feedback.
Write a Java program to implement a test case that uses assertTrue with a custom message to clearly indicate the nature of the failure.
Write a Java program to design a test case that combines multiple assertions with descriptive custom messages for each check.
Write a Java program to construct a test case that uses custom assertion messages to display both expected and actual values when a test fails.

Go to:

PREV : Ignore Test Case Scenario.
NEXT : Test Private Methods.

Java Code Editor:

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