Unit Testing vs Integration Testing: What are the key differences?
Imagine you open a shopping website, browse around and see some products of your liking. After placing them in the cart, you're all ready to check out, only to discover that your favorite items are nowhere to be found on the list. This is one of many examples of a software bug that could be caught using integration testing.
There are multiple testing stages that software goes through before release, the two most popular being unit and integration testing. Unit testing is the first phase of testing and integration is done when the software goes beyond the modular level
In this article, we’ll explore these types of testing, the difference between unit testing and integration testing, their benefits, use cases, and best practices.
What is unit testing?
Unit testing is a software testing method where individual units or components of a software application are tested to ensure that each unit works as intended. It involves the creation of small, isolated tests for units of code to verify their functionality. These tests are run regularly to catch and fix any bugs early on in the development process before they become more difficult and expensive to resolve.
Unit testing is a key component of Agile software development methodologies, such as Scrum and Kanban, as it allows for continuous integration and delivery of small, working increments of code. Once all units in a program are error-free and meet their requirements, larger components can be evaluated by means of integration testing.
What is integration testing?
Following unit testing is integration testing - the second level of the software testing process. In integration testing, different components or modules are combined and tested as integrated units. While unit testing focuses on individual code units in isolation, integration testing aims to identify any bugs or clashes that can arise when multiple components interact with each other.
Independent modules can work smoothly on their own, but once integrated, they can be incompatible and collapse with one another. Failures may stem from inconsistent code logic, shifts in requirements, erroneous data, or other various reasons. Integration testing prevents software from such downfalls, making sure that the unit-tested code builds work together in harmony post-integration.
Verifies the implementation and behavior of individual units separately
Verifies the interactions and behavior of multiple modules working together
Functions, methods, classes, or modules
Interactions between components, systems, and databases
Can be performed in a controlled, isolated environment
May require a more realistic, representative testing environment to accurately test interactions
Usually executed by developers
Can be performed by developers or a dedicated QA team
White box testing: Requires in-depth exposure and access to the code
Black box testing: doesn’t require knowledge about the internal design or the code structure
Typically easier and takes less time as the scope is limited
Can be more complex with longer debugging time as it covers a broader part of the application
Less expensive than integration testing, as it requires little setup to run the tests, and they take little time to execute
More costly as it may require a more complex testing environment and high maintenance
How do unit testing and integration testing improve software quality?
Benefits of unit testing
The benefits of unit testing include:
- Lightweight and fast: The execution speed of unit testing is one of its important advantages. These tests are designed to run independently without impact or dependencies on other systems, such as file access or network capabilities.
- Improved code quality: Unit testing helps identify and fix bugs early in the development process, resulting in higher-quality code.
- Facilitated refactoring: Unit tests provide a safety net for code changes, making it easier to refactor and improve code without introducing new bugs.
- Better documentation: Unit tests serve as documentation of how the code should behave, making it easier for new developers to understand and maintain the code.
- Increased CI/CD velocity: In the CI/CD pipeline, tests should be fast and frequent, which can be achieved through unit testing. By breaking the code down into small, testable units, developers can quickly validate their changes.
Examples of unit testing
Consider a software system that allows users to place orders on an e-commerce website. Unit testing for this system would involve testing individual units, such as adding products to the cart, calculating the total cost, and processing payment.
Testers would write test cases to verify each unit. For example, for the unit of adding products to the cart, the test case might specify inputs of a product name, price, quantity, and expected outputs of successful addition. Similarly, unit testing will verify that the cost calculation unit correctly calculates the total amount. That is, for an item with a price of $10 and a quantity of 2, the software should return the output of $20, not any other results.
Benefits of integration testing
- Better integration with third-party components: Integration testing helps to ascertain that the system integrates smoothly with third-party components, such as APIs or libraries, which may not be done in unit testing.
- Early detection of integration bugs: Integration problems can be caught early in the development cycle when they are easier and less expensive to fix. This helps to avoid costly and time-consuming rework later on.
- Improved system reliability: Integration testing verifies if integrated units function properly as a whole and align well with specified requirements. This leads to a more stable system that is less likely to fail in production.
- Better scalability: Integration testing ensures that a system is scalable and maintainable by verifying interoperability and identifying performance bottlenecks, and dependency issues
Example of integration testing
Using the E-commerce site example, integration testing would focus on the interactions between components. Specifically, a test case for the integration between the component that adds items to the cart and the component of calculating the total cost might specify inputs of adding multiple products to the cart and expected outputs of the correct calculation of the total cost.
Unit testing and integration testing best practices
Combine Unit and Integration Testing
The concept of the "test pyramid" can be useful in understanding how unit and integration testing fit into a broader testing strategy. There is not a single step of the testing process that is more important than the other. Using unit and integration testing together helps to achieve a healthy balance between fast feedback, comprehensive coverage, and cost-effectiveness in your testing strategy.
Read more: The Evolution of the Testing Model and Where It Will Go Next
Automate the testing process
While regression testing is critical each time the units are integrated, executing it manually can be repetitive and time-consuming. Automated tests, on the other hand, can be run more efficiently, providing fast and reliable feedback on the state of the code.
Test often and early using CI/CD
When unit and integration tests are integrated into the CI/CD pipeline, every change to the code is automatically tested and deployed. This makes it easier to identify and fix bugs early in the development cycle, ensuring that changes are thoroughly tested before they are released to production.
Both forms of testing are essential to maintain the quality and reliability of an application. With the ever-evolving software landscape, it's important for developers to stay up-to-date with best practices and tools for testing, such as continuous integration, mocking, and test automation frameworks. By utilizing these techniques, developers can minimize the risk of bugs and enhance the overall user experience. Ultimately, investing time and resources in unit and integration testing will pay off in the long run, delivering a high-quality and reliable software application.
Katalon Platform - Software Quality Management Platform
Performing integration testing typically involves UI and API integration testing. However, professionals may not be able to perform those tests in one place and have to constantly switch from 1 tool to another for every different AUT.
The Katalon Platform is a powerful all-in-one platform to help QA teams plan, design, run and debug automated API and UI integration test cases.
Hours spent on building your own automation engine can be used for the testing itself. As a hybrid testing framework built upon Selenium and Appium, Katalon supports different testing methodologies, including
- Data-driven testing (DDT)
- Behavior-driven development testing (BDD)
- Keyword-driven testing
Auto-triggered tests on CI
Katalon's integrations with tools such as Circle CI, Jenkins, and GitLab allow test cases to be automated and run as part of the CI/CD pipeline. Wire up end-to-end UI and API to automatically trigger and run, ensuring that integration issues are detected and addressed early.
Easy deployment with Docker containers
Users can easily set up and run Katalon integration tests in a Docker environment, allowing them to test how their application interacts with other components in a controlled and isolated environment. Katalon allows you to bundle your test execution into virtual containers. For example, building a Docker image to execute your test with a specific environment.
Reduce test maintenance effort
Following the page object design model, Katalon provides a centralized repository for not only designing but also managing your test cases and their artifacts. Locators are stored across tests in an object repository. When your UI changes, clicks are all it takes to get your automation scripts up and running again.