JUnit Calculator Test Case Example

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topsupmiluser2027

November 12, 2026

On November 12, 2026

JUnit Calculator Test Case Example

We will examine a Simple Calculator Test case example for writing JUnit Tests. This tutorial helps beginners understand how to write and execute JUnit Tests.

Calculator class

The Calculator class is the class to be tested. The class contains mathematical methods, including adding, subtracting, multiplying, and dividing. We will write JUnit test methods to test these methods.

Steps to create a Calculator Java class:

Create Calculator Java class

Calculator User Story

Sample User Story in Agile scrum story card format :

Calculator User Story

JUnit Test Mechanism

The @Test annotation methods test the Calculator object under test.

Junit Calculator Test case example

Arrange-Act-Assert pattern

AAA pattern for writing unit tests for the method under test. AAA stands for:

Arrange
Act
Assert

Arrange – set up, create objects, data, etc

Act – Invoke the method under test

Assert – Verify pass or fail

Calculator Test Case

The below example shows some basic sample JUnit test cases.

package com.testingdocs.calculator.tests;

//Arrange-Act-Assert pattern
import com.testingdocs.calculator.Calculator;
import org.junit.Test; 
import org.junit.Assert; 
import org.junit.Before;

public class CalculatorTest {
private Calculator objCalcUnderTest;

@Before
public void setUp() {
//Arrange
objCalcUnderTest = new Calculator();
}

@Test
public void testAdd() { 
int a = 15; int b = 20; 
int expectedResult = 35;
//Act 
long result = objCalcUnderTest.add(a, b);
//Assert
Assert.assertEquals(expectedResult, result);
}

@Test
public void testSubtract() {
int a = 25; int b = 20; 
int expectedResult = 5; 
long result = objCalcUnderTest.subtract(a, b);
Assert.assertEquals(expectedResult, result);
}

@Test
public void testMultiply() {
int a = 10; int b = 25;
long expectedResult = 250;
long result = objCalcUnderTest.multiply(a, b);
Assert.assertEquals(expectedResult, result);
}

@Test
public void testDivide() {
int a = 56; int b = 10; 
double expectedResult = 5.6; 
double result = objCalcUnderTest.divide(a, b);
Assert.assertEquals(expectedResult, result,0.00005); 
}

@Test(expected = IllegalArgumentException.class)
public void testDivideByZero() { 
int a = 15; int b = 0;
objCalcUnderTest.divide(a, b);
} 
}

Screenshot

Screenshot of the tests in Eclipse IDE.

Calculator Test case Â

Right-click the JUnit test example class and run the test methods as “JUnit Test”.Â

In this example, we have placed the Calculator class( the test class intended to be tested) in the same package as the test-case example class. However, this might not be the case while writing real tests. The application source code can be separated from the test or automation code.