Ultimate Guide to Integration Testing vs. Unit Testing in 2024

Businesses and developers use various software testing methods to deliver high-quality software. 

Finding errors during the testing stage is seven times less expensive than the production stage of software.¹ Therefore, using the suitable testing method for the proper case is crucial for quality assurance teams (QA).

Unit testing and integration testing are essential testing practices for software applications. It is important for QA teams to know the differences between the two since each practice uses different methods and is executed at different stages of software testing.

This article aims to compare integration and unit testing and pay attention to their differences, benefits, and when to use them.

What is the key difference between integration testing and unit testing?

The main difference between integration and unit testing is that they are used at different stages of the development process and have different goals. Unit testing focuses on individual code units, while integration testing focuses on how they work together.

Table 1: A summary of integration testing vs. unit testing

What is integration testing?

Integration testing is a method of testing how different units of code work together. The goal of integration testing is to ensure that the integrated system behaves as expected and that there are no conflicts or errors between different code units.

What is unit testing?

Unit testing is a method of testing individual code units, such as functions or practices, in isolation from the rest of the system. Unit testing aims to ensure that each unit of code works as intended and to identify any bugs early in the development process.

See the testing pyramid below (Figure 1) to see the place of integration and unit testing in the levels of software testing.

Figure 1: Testing Pyramid

Source: Medium²

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Top 6 Benefits of Integration Testing

Integration tests have several benefits, including

1. Detection of integration issues: An integration test can help identify issues that may arise when different components or systems are integrated, enabling validation of the system.
2. Improved system functionality: Integration testing helps ensure that all system components work together as expected.
3. Improved scalability and performance: Integration testing can help identify issues with scalability and performance before the system is deployed to production.
4. Improved reliability: Integration testing ensures the system can handle real-world usage scenarios.
5. Enables testing of interfaces and protocols: Integration testing allows testing of interfaces and protocols between different systems.
6. Enables testing of end-to-end scenarios: Integration testing enables end-to-end scenarios, that is, testing the system from the user’s point of view.

To get an in-depth understanding of integration testing, read our article ‘Integration Testing in 2023: Importance, Types & Challenges’

When should you use integration testing? 

Integration testing is typically used during the development of software, specifically in the following situations:

1. Developing complex systems: Integration testing is essential for complex systems with many components that need to work together seamlessly.
2. Developing new features: Unit tests should be written to test new code before deployment to production. This is also known as Test-Driven Development (TDD). TDD is a software development methodology where you write tests before writing the actual code; unit testing is an essential part of this methodology. 
3. Developing distributed systems: Integration testing is essential for distributed systems where components are located on different networked computers. Integration tests will help ensure that all the components communicate correctly.
4. Refactoring existing code: Unit tests can ensure that changes to the code do not introduce new bugs, so it is best to test when refactoring the code. Unit tests can also help ensure that code changes by different developers do not break existing functionality.
5. Working with third-party libraries or APIs: Integration testing is essential when working with third-party libraries or APIs to ensure that they are integrated correctly and working as expected.
6. Performing regression testing: Integration testing can be used to ensure that the changes made in the system do not break the integration of the already integrated components.

When should you use Unit Testing?

1. Bug Fixing: After identifying a bug and before fixing it, write a failing unit test that replicates the issue. Once you’ve fixed the bug, this test should pass, serving as a regression safeguard.
2. Continuous Integration: Integrate unit tests into your Continuous Integration (CI) pipeline to automatically catch issues before they get to production.
3. Code Reviews: Including unit tests as part of the code review process sets a good practice and ensures that tests are written and updated as the codebase evolves.
4. Documentation: Well-written unit tests serve as a form of documentation by example, explaining how a particular piece of functionality is supposed to work.
5. Performance Tuning: Use unit tests to measure performance metrics for small units of code. This can be helpful in identifying bottlenecks.
6. Library/SDK Development: When developing a library or SDK, unit tests are essential for ensuring that each small component works as expected, independent of external dependencies.
7. Team Onboarding: When new developers join the team, unit tests can help them understand how existing pieces of code are expected to behave.
8. End-of-Sprint Verification: Run unit tests at the end of each development sprint to ensure all features and fixes for that sprint have not broken existing functionality.
9. Validation of External Inputs: Use unit tests to validate that your code correctly handles a variety of inputs, especially if those inputs are coming from external sources.
10. Safety-Critical Systems: In systems where failure is not an option (e.g., medical, aviation), unit tests are an essential part of the development process to minimize risks.
11. Regular Maintenance: As software evolves, unit tests can confirm that existing features still work as new ones are added, or existing ones are modified.
12. Learning and Skill Enhancement: Writing unit tests helps developers to think critically about code structure and design patterns, thereby improving their software engineering skills.

Whether to use unit testing depends on the project’s complexity, team size, the nature of the codebase, and the development process.

Read our ‘10 Unit Testing Best Practices’ article to learn more about unit testing.

If you want to learn more about quality assurance, reach us;

External links

• 1. “The True Cost of a Software Bug: Part One” Celerity
• 2. Lawrence Tan “Unit Tests, UI Tests, Integration Tests & End-To-End Tests” Medium, September 19, 2019