Java Unit Test Case: Asserting Expected method returns

Java Unit Test: Exercise-1 with Solution

Write a Java unit test case to assert that a given method returns the expected value.

Sample Solution:

Java Code:

// Calculator.java
public class Calculator {
    public int add(int a, int b) {
        return a + b;

// CalculatorTest.java

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

import static org.junit.Assert.assertEquals;

public class CalculatorTest {

    public void testAdd() {
        // Arrange
        Calculator calculator = new Calculator();

        // Act
        int result = calculator.add(3, 5);

        // Assert
        assertEquals(8, result); // The expected value is 8

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


The above Java code is a JUnit test class (CalculatorTest) for testing a hypothetical "Calculator" class. The code uses JUnit's annotations and classes to define a test case and run the tests. Let break down the key components:

  • Test Method:
    • @Test Annotation: Indicates that the following method is a JUnit test case.
    • Arrange: Sets up the test scenario, including creating an instance of the "Calculator" class.
    • Act: Calls the "add()" method on the "Calculator" instance with specific input values (3 and 5).
    • Assert: Uses the assertEquals method to verify that the result of the "add()" method is equal to the expected value (8).
  • Main Method:
    • JUnitCore.runClasses: Invokes JUnit to run all the test methods in the specified class (CalculatorTest.class).
    • Result: Holds the result of the test execution, including information about passed and failed tests.
    • Checking Failures: If there are failures, it prints a message indicating that the tests failed and provides details about each failure. Otherwise, it prints a success message.


Flowchart: Java Unit Test Case: Asserting Expected method returns.
Flowchart: Java Unit Test Case: Asserting Expected method returns.

Java Code Editor:

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