Java Integration Testing​: A Step-by-Step Guide

You can’t go without different types of testing in any software project. A diverse set of tests is needed to make sure that the final product corresponds with all the functional and non-functional requirements. 

In this article, we discuss integration tests in Java solutions. You’ll learn why they are important, how to conduct the process, and discover best practices and tools you can use for keeping complex software systems working as intended.

What Is Integration Testing?

Let’s start with the definition. Integration testing is the type of functional testing that checks separate units of a software system working as a group. In other words, the goal of integration testing is to verify interactions between components and their ability to operate as a single entity. This is like checking that all parts of a car are compatible with each other, and that the car, when assembled together from these parts, drives properly. 

It’s critical to control integrations in Java solutions with microservices architectures because there are many complex interactions between modules and components.

Types of integration testing

Integration testing is divided into two types: Big Bang and incremental. The incremental type can be further divided into three approaches: bottom-up, top-down, and sandwich (or hybrid).

The Big Bang approach means that you should first connect all the existing components and then check the whole software system. This method is beneficial because it takes little planning and provides a holistic view of the system’s operation. The main drawback of this strategy though is that, because all the components are integrated at the same time, it may be difficult to determine the root cause of a failure. Furthermore, since checking doesn’t start until all modules have been written, there might not be enough time for comprehensive checks, particularly in bigger systems.

On the contrary, incremental methodology is a step-by-step process. 

Differences Between Integration and Unit Testing

Unit testing is the very first step of software verification. It checks isolated units of code (functions, methods, classes, modules) before their integrations are put under control. 

How to Do Integration Testing in Java​

We provide a brief tutorial on how to verify integrations in Java projects.

Best Practices for Integration Testing in Java

A number of variables, including the team’s expertise and the best practices they employ, affect how well testing goes. Let’s talk about the tried-and-true methods that can improve your software testing and development process.

Dependency injection for modular design

Dependency injection (DI) is a technique for maintaining the flexibility and organization of your code. This method helps examine each module independently (without external counterparts).

Therefore, you can inject dependencies at runtime rather than hardcoding them into your classes. For example, if you have a UserService that depends on a UserRepository, you can pass the repository into the service rather than creating it inside the service itself. This makes it very simple to swap out the repository with a mock version and inspect UserService in isolation.

Test-driven development (TDD)

Many Java developers follow the TDD practice to avoid errors in their code. This is like writing a recipe before cooking: you design tests that specify what your code should do first, and then you write the code to make those verifications pass.

For instance, if you’re building a payment processing feature, you might write tests for different payment scenarios first (like successful payments, failed payments, etc.). When developing a payment processing functionality, for example, you may initially design tests for various payment situations (successful payments, unsuccessful payments, etc.). By doing this, you can prevent integration issues later on, as you consider how everything works together right away.

Mocking frameworks

Sometimes you don’t want to deal with real dependencies like databases or external services. That’s where mocking frameworks like Mockito come in handy. If you’re testing a service that fetches user data from an API, you can create a mock version of that API, instead of hitting the actual API (which could be slow or unreliable). This way you can simulate different responses and check how your service behaves without any outside interference.

Clean and isolated test environment

Let’s say you want to plant a beautiful garden, but your yard is overrun with trash and weeds — there is little chance that your plants will thrive! The same is true for testing; having a clean and isolated environment is essential.

If you want the tests to show accurate results, the environment should be very similar to the production environment. You should configure databases, APIs, and other services similarly to how they would operate in production. For example, if you’re using Docker, you can create containers that replicate your production setup. This way, when you run your integration tests, you’re more likely to catch issues that would occur in the real world.

Testing of critical modules

Not every component of your application is equally important; some are more crucial than others. Check these important areas first. For example, if your app has a payment processing module, make sure it gets plenty of attention in your integration tests, as any malfunction here could cause serious problems for consumers. Review these crucial cases anytime adjustments are made to guarantee everything continues to go smoothly.

Top Java Integration Testing Frameworks

Developers and QA specialists use some popular frameworks and libraries for integration testing.

Spring Test

Spring Test is a module of the Spring Framework. It is widely used to write and execute integration tests for Spring Boot applications. You can control database integration, application context, and the correctness of the interactions between application layers (controllers, services, repositories) in the context of a Spring container.

Using the Mockito library, Spring Test mocks external services and dependencies. It also reuses application contexts across tests to reduce setup time and automatically rolls back transactions after each check to maintain data integrity. The framework can simulate HTTP requests and validate responses with no web server. One more important feature is its integration with JUnit (4 and 5) and TestNG.

JUnit

One of the most widely used frameworks in the Java environment is JUnit. It is more frequently used for unit testing, although integration testing can also benefit from its adaptability and interaction with other tools. JUnit adapts to different needs, from database checks to API validations. It also works well with frameworks (Spring, Testcontainers, Hibernate) and CI tools (Jenkins, GitHub Actions). JUnit 5 introduces a modular architecture allowing custom extensions and better support for Java 8 features.

An integration test in a Spring Boot application might use JUnit to verify that a REST endpoint correctly retrieves data by asserting the response against expected values.

TestNG

TestNG, which stands for “Next Generation,” is inspired by JUnit and is widely used in the Java world. The framework is great not only for unit but integration testing as well thanks to its ability to handle complex workflows and dependencies. Configuration capabilities (e.g., grouping), parallel execution, dependency management, and detailed reports make TestNG suitable for large-scale solutions. The framework can work with Spring, Maven, Jenkins, Gitlab, Github, Testcontainers, and other tools, which is good for real-world applications.

Arquillian

Arquillian is created specifically for Java EE applications. The framework runs tests in the actual application server or container, so you’re checking your code in the same environment it will run in production. It supports many different containers (e.g., WildFly, Payara, Tomcat), works with popular frameworks and tools (e.g., Hibernate, Spring, MicroProfile, JUnit), and can check everything from database interactions to REST endpoints and messaging systems. Arquillian automates packaging, deployment, teardown, and other complex tasks.

JWebUnit

The JUnit extension for web application integration testing is called JWebUnit. This framework, which mimics user interactions with web programs, is based on Java and has a straightforward API. You can check that form submissions, page navigation, user authentication, and other workflows are operating correctly. You can also check the interaction between the frontend (HTML, forms, navigation) and the backend (business logic, database). JWebUnit integrates with other frameworks and automation tools (HtmlUnit, Selenium) to be part of holistic web testing services.

Testcontainers

This Java library has lightweight APIs for managing Docker containers. Developers use it to run integration tests against real services (databases, message brokers) in isolated environments. Such isolation prevents data conflicts and ensures a clean state. You can incorporate Testcontainers into existing test suites because it works with JUnit and other frameworks.

When checking integrations with Testcontainers, you would start a PostgreSQL database in a Docker container before running your tests that interact with it. Once the verification is finished, Testcontainers automatically cleans up the container from leftover data that could impact future verifications.

WireMock

If you need to stub or mock web services during tests, use WireMock. This library can create mock responses for HTTP requests based on specified criteria and record real service interactions and replay them in tests. That’s why it is possible to conduct tests without actual external services.

For example, in an application that interacts with a third-party payment service, WireMock can be used to stub the payment API. Thus, developers don’t need access to the real payment service to check various scenarios (e.g., successful payments or failures).

Why Choose SaM Solutions for Java Integration Testing​?

SaM Solutions’ experts have vast experience in quality assurance and Java development. Our QA team uses the best new tools and proven methods to check software integration, as well as other functional and non-functional aspects. We offer custom services, which means tight and transparent collaboration with our clients for the achievement of perfect results.

Conclusion

What are integration tests in Java​ projects? These are important verifications that make all the parts of software solutions work together properly. What do you need to conduct integration testing at a high level? Hire SaM Solutions’ specialists and enjoy the best outcomes in your project.