10 Best Automated Unit Testing Tools for Java

In today’s world of continuous software development, maintaining code quality while rapidly pushing out features and bug fixes is a constant challenge. With its enterprise-grade capabilities and robust ecosystem, Java consists of complex codebases where a seemingly insignificant change can lead to massive ripple effects throughout the application. This complexity makes unit testing not just a best practice but a crucial foundation for sustainable software development.

As the first line of defense in your codebase, unit testing tests individual blocks of code, helping you catch issues early in the development cycle when they are the least expensive to fix.

In this blog, we’ll explore the fundamentals of unit testing, learn about automating this process, and evaluate the top 10 contenders that provide automated unit testing capabilities in Java.

What is Unit Testing

A unit represents the program’s smallest testable part, typically a function, method, or class. You can think of it as a single gear in a complex machine that aims to accomplish a specific task. You are testing to see if that particular machine gear works as expected.

Let’s consider an example.

Bob wants to calculate the amount of tax he needs to pay. For that, he writes a script in Java using JUnit:

public class TaxCalculator {
private static final double TAX_RATE = 0.2;public double calculateTotalPrice(double basePrice) {
if (basePrice < 0) {
throw new IllegalArgumentException("Base price cannot be negative");
}
return basePrice + (basePrice * TAX_RATE);
}
}

Now he can test if his script is working as expected by running this test:

@Test
public void calculateTotalPrice_WithPositivePrice_ReturnsPriceWithTax() {
// Arrange
double basePrice = 100.00;
double expectedTotal = 120.00; // 100 + (100 * 0.2)// Act
double actualTotal = calculator.calculateTotalPrice(basePrice);// Assert
assertEquals(expectedTotal, actualTotal, 0.01);
}

But what if he accidentally puts a negative value in his calculator? Thankfully, he had already thought about this. He can test if the behavior he added is working as intended:

@Test
public void calculateTotalPrice_WithNegativePrice_ThrowsException() {
// Arrange
double basePrice = -50.00;// Act & Assert
assertThrows(IllegalArgumentException.class, () - > {
calculator.calculateTotalPrice(basePrice);
});
}

Now that Bob has this test setup, he can best rest assured that while filing his taxes, his program won’t break when he gives a negative number to the calculator.

Automated Unit Testing

Looking at Bob’s example, you might notice a potential issue: each test case requires writing a separate function, setting up test conditions, and running tests manually. As his tax calculation grows more complex – perhaps adding different tax brackets, deductions, or special rules – the number of test cases would multiply. Manually managing all these tests would be time-consuming and error-prone.

This is where automated unit testing comes to the rescue. Instead of manually running each test, Bob can transform his testing process into a streamlined, automated workflow that runs with a single command. Here’s how you can do this using JUnit:

// Test multiple negative values at once
@ParameterizedTest
@ValueSource(doubles = {-50.00,
-100.00,
-1.00
})
void calculateTotalPrice_MultipleNegativeValues(double basePrice) {
assertThrows(IllegalArgumentException.class, () - > {
calculator.calculateTotalPrice(basePrice);
});
}

Top Automated Unit Testing Tools for Java

1. JUnit

JUnit is an open-source framework for writing and running unit tests in Java. It is considered a standard in the Java testing community. It promotes test-driven development (TDD), where developers write the tests before implementing the actual code.

Various Java IDEs like Eclipse, NetBeans, and IntelliJ IDEA support it.

JUnit has three important classes:

• Assert – verifies logic with a boolean expression (true or false).
• TestCase – a class that groups together a set of similar tests. Replaced by the @Test annotation in recent versions.
• TestResult – a class that collects the results of executing test cases. Replaced by the TestExecutionListener class in recent versions.

Example snippet –

import org.junit.Test;
import static org.junit.Assert.*;public class StringUtilsTest {
@Test
public void testReverse() {
StringUtils utils = new StringUtils();
assertEquals("olleh", utils.reverse("hello"));
}
}

2. Selenium

Unlike JUnit, Selenium is more of a testing library than a framework. It is an open-source tool for testing web applications across different browsers and programming languages, including Java. A tool is considered to be a framework when it acts as a ready-to-use toolkit, whereas a library only has reusable blocks of code that the user has to implement manually.

Thus, Selenium gives users much more granular control over how they wish to set up the testing logic.

It consists of the following components:

• User-defined code – consists of instructions and commands interacting with the browser and other web elements.
• Client library – acts as a bridge between user code and WebDriver.
• WebDriver – API that defines custom instructions for the internet interface. For example, ChromeDriver for Chrome.
• Browser – application where the web code runs.

Example snippet –

import org.junit.Test;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import static org.junit.Assert.assertEquals;@Test
public void testPageTitle() {
WebDriver driver = new ChromeDriver();
driver.get("<https://www.example.com>");
assertEquals("Example Domain", driver.getTitle());
driver.quit();
}

3. Spring Test

Spring is a comprehensive and widely adopted framework for developing enterprise-level Java applications. It offers a robust ecosystem for building scalable and maintainable software, with a particular focus on web applications. The framework’s popularity stems from its modular architecture, which allows developers to choose and integrate specific components as needed.

It also bundles its own testing module inside the framework to simplify the process of writing and executing tests for Spring-based projects.

There are two main components in Spring Test:

• TestContext Framework: the core of Spring Test, providing annotation-driven unit and integration testing.
• Spring Boot Test: an extension of Spring Test offering additional capabilities.

Example snippet –

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import static org.assertj.core.api.Assertions.assertThat;@SpringBootTest
class UserServiceTest {
@Autowired
private UserService userService;@Test
void testCreateUser() {
User user = userService.createUser("John", "[email protected]");
assertThat(user).isNotNull();
assertThat(user.getName()).isEqualTo("John");
}
}

4. TestNG

TestNG is another robust open-source unit testing framework for Java that extends the existing capabilities of frameworks like JUnit and NUnit. It is designed to test various needs, including unit, functional, end-to-end, integration, etc.

It uses a rich set of annotations on top of existing annotations in JUnit, such as @BeforeGroups and @AfterGroups, which allow for better organization and flow of control.

There are three main key components in TestNG:

• Annotations – unique markers of labels that provide metadata about a program. For example, @Test, @BeforeTest, etc.
• XML Configuration – a testing.xml file defines test groups, execution order and parameters.
• Test Groups – organizes tests into logical units.

Example snippet –

import org.testng.annotations.Test;
import org.testng.Assert;public class SimpleTest {
@Test
public void testAddition() {
int result = 2 + 2;
Assert.assertEquals(result, 4, "Addition result is incorrect");
}
}

5. Mockito

Mockito is an open-source framework widely used for automated unit testing in Java with the creation of mock objects, which are simulated objects mimicking the behavior of real objects in a controlled way. This technique allows the code being tested to be isolated from its dependencies.

It includes a lot of boilerplate code in its test setup, making tests more readable and maintainable.

Its key components include:

• Mock Creation: creates mock objects for classes and interfaces.
• Behavior Stubbing: defines specific behavior for the mock objects.
• Verification: verifies whether certain methods were called on mock objects, supporting behavior-driven testing.

Example snippet –

import static org.mockito.Mockito.*;
import static org.junit.Assert.*;
import org.junit.Test;public class SimpleTest {
@Test
public void testUserService() {
UserRepository mockRepo = mock(UserRepository.class);
when(mockRepo.findUserById(1)).thenReturn(new User("John"));
UserService service = new UserService(mockRepo);
assertEquals("John", service.getUsernameById(1));
verify(mockRepo).findUserById(1);
}
}

6. Selenide

Selenide is a powerful testing library built on top of Selenium WebDriver and designed specifically to simplify and streamline UI testing in Java. It provides a much simpler and readable API than Selenium, making it much more manageable and approachable for beginners.

Because it can handle the browser’s lifecycle automatically, it eliminates the need to manually set up and tear down WebDriver instances.

Its key components include:

• Simplified API: offers concise and readable API, reducing boilerplate.
• Automatic WebDriver Management: eliminates the need for manual setup of drivers.
• Smart Waits: built-in wait mechanisms ensure elements are ready before interactions.

Example snippet –

import static com.codeborne.selenide.Selenide.*;
import static com.codeborne.selenide.Condition.*;
import org.testng.annotations.Test;public class TodoListTest {
@Test
public void userCanManageTodoList() {
open("<https://lambdatest.github.io/sample-todo-app/>");
$("li:nth-child(1) .checkbox").click();
$("li:nth-child(3) .checkbox").click();
$("#sampletodotext").setValue("New Item").pressEnter();
$$("li").last().shouldHave(text("New Item"));
int pendingCount = $$("li").filter(not(cssClass("completed"))).size();
System.out.println("Pending items: " + pendingCount);
}
}

7. REST Assured

REST Assured is an open-source Java library for testing, with a specific focus on REST (representational state transfer) web services. It provides a domain-specific language (DSL) that simplifies the process of writing and executing tests for RESTful APIs.

The library supports various HTTP methods, including GET, POST, PUT, DELETE, OPTIONS, PATCH, and HEAD, allowing comprehensive testing of API endpoints.

Its key components are –

• Request Specification – defines the details of the HTTP request to send to the API.
• Response Specification – helps validate the API response.
• Matchers, Filters, and Extractors – methods for verifying a particular outcome. for example equalTo(), containsString() etc.

Example snippet –

import static io.restassured.RestAssured.*;
import static org.hamcrest.Matchers.*;
import org.testng.annotations.Test;public class SimpleApiTest {@Test
public void testGetRequest() {
given()
.baseUri("<https://reqres.in/api>")
.contentType("application/json")
.when()
.get("/users/2")
.then()
.statusCode(200)
.body("data.id", equalTo(2))
.body("data.email", equalTo("[email protected]"))
.body("data.first_name", equalTo("Janet"))
.body("data.last_name", equalTo("Weaver"))
.body("data.avatar", notNullValue());
}
}

8. JBehave

As the name suggests, JBehave is a Behavior-driven development (BDD) framework for automated unit testing in Java. It allows users to write tests in natural language so that both technical and non-technical people can understand them.

It focuses on describing an application’s behavior from a user’s perspective rather than testing specific methods or classes.

Key components of JBehave include –

• Stories: files with .story extension that define application behavior
• Steps: methods annotated with @Given, @When, or @Then
• Runners: classes that actually run the story. For example, JUnitStory, Embedder, etc.

Example snippet –

import org.jbehave.core.annotations.When;
import org.jbehave.core.annotations.Given;
import org.jbehave.core.annotations.Then;public class CalculatorSteps {
private Calculator calculator = new Calculator();
private int result;@When("I add $a and $b")
public void whenIAddNumbers(int a, int b) {
result = calculator.add(a, b);
}
}

9. Spock

Spock is a testing and specification framework for Java. It is powered by Groovy, a scripting language that runs on the Java Virtual Machine (JVM). It strips away many of the traditional methods you would expect in a testing framework, such as assertions, record/replay mocking API, and superfluous annotations, in favor of question-based testing.

It also follows an open-minded approach to testing, restricting you to techniques like test-first, test-last, behavior-driven, etc.

Spock has the following key components:

• Specifications: classes written in Groovy that define the expected behavior.
• Blocks: structural elements like given: , when: , then: etc.
• Extensions: for adding custom functionality to tests.

Example snippet –

import spock.lang.Specification
import spock.lang.Unrollclass CalculatorSpec extends Specification {
@Unroll
def "should calculate sum correctly"() {
given:
def calculator = new Calculator()expect:
calculator.add(a, b) == result

where:
a | b || result
1 | 2 || 3
5 | 3 || 8
}
}

10. Parasoft JTest

Parasoft JTest stands out as an AI-powered Java testing tool in this list. It’s designed to enhance code quality, security, and reliability. It leverages AI algorithms to generate comprehensive JUnit test suites, which help accelerate the process of reaching hidden code coverage tests and validating functionality.

It is an integrated development testing solution, meaning it can automate a wide range of coding best practices, generate analysis reports, and more.

It has many components, including:

• Unit Test Assistant: provides insights to enhance test stability and extend test cases.
• Static Code Analysis: verifies code quality and compliance standards
• Customizable Rule Sets: allows tailoring of tests to specific coding guidelines

Example snippet –

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;
import static org.mockito.Mockito.*;public class ParasoftJtestExample {
@Test
public void testRequestLoan() throws Throwable {
DownPaymentLoanProcessor underTest = new DownPaymentLoanProcessor();
double availableFunds = 0.0d;
double downPayment = 0.0d;
double loanAmount = 0.0d;
LoanRequest loanRequest = LoanRequestFactory.create(availableFunds, downPayment, loanAmount);
// Additional test logic would be generated here
}
}