Unit Testing vs Integration Testing: What is The Difference?

Unit testing vs integration testing, what are their differences? Which one to choose? These are difficult questions for many people. In this blog, we will introduce in detail what unit testing and integration testing are and clarify their differences.

What is a Unit?

A unit is the smallest logically isolated code block. Unit testing is a type of testing that focuses on isolating and testing the smallest possible fragments of code. So, what exactly is a unit?


The term "unit" comes from mathematics. The number 1 is considered a unit because it is the smallest natural number. It is the smallest positive integer. Similarly, a unit in your source code is the smallest logically separate code fragment, a complete and distinct portion.

In most programming languages, your unit would be a function or method call. The benefit of unit testing lies in the fact that if your code is composed of independent small pieces, writing tests for them becomes relatively easy. This ease of writing translates to completing unit testing alongside the development of features.

Compared to other forms of testing, unit testing has short execution times. This means you can run unit tests frequently. As the software matures, a suite of unit tests becomes a powerful tool to prevent regressions and reduce maintenance costs.

What is Unit Testing

When considering adding unit tests to existing software, it's important to consider the cost and benefits.

A key assumption of unit testing is that the software being tested can be easily broken down into different units. This assumption often doesn't hold in software that was not designed with unit testing in mind. Adding unit tests to existing software is typically a great way to stabilize it and prevent future regressions. However, refactoring the code to support simple unit testing may require significant effort and may even introduce new defects. When considering adding unit tests to existing software, the cost and benefits need to be carefully weighed. If your code is working, requires minimal changes, or is not easily testable, the benefits of adding unit tests may not outweigh the costs. In such cases, relying on integration testing can help prevent defects in that area.

What is Integration Testing?

Integration testing focuses on the entire software stack. If the philosophy behind unit testing is based on the idea that testing small, independent code fragments is a good way to prevent regressions, integration testing is based on the understanding that things usually go wrong at the boundaries. The external world is a messy place, and the places where it interacts with your code are often where unexpected things happen.


You can achieve 100% code coverage with unit tests and still discover failures in your software. You might attempt to read a file from the wrong location, or your software may receive unexpected output from a called service, or it may make an invalid database call.

While unit tests should be fast and numerous, a good integration testing strategy should focus on a smaller number of high-impact tests. These tests should span all boundaries that unit tests cannot cross, such as writing to the file system, interacting with external resources, and so on.

Unit Testing vs Integration Testing: Key Differences Compared

Unit Testing

Integration Testing

Focuses on testing individual units or components of code.

Focuses on testing the interaction and integration between multiple units or components.

Tests the smallest logical code blocks, such as functions or methods.

Tests the combined functionality of multiple units working together.

Isolates units from dependencies using mocks or stubs.

Integrates units with their actual dependencies and external systems.

Aims to validate the correctness of individual units in isolation.

Aims to validate the interaction and cooperation between units.

Helps identify bugs or issues within specific units.

Helps uncover bugs or issues arising from the integration of units or the interaction with external systems.

Provides faster feedback as tests execute quickly.

May take longer to execute as it involves testing multiple units and their interdependencies.

Typically written by developers during the development process.

Typically involves collaboration between developers, testers, and other stakeholders.

Provides a safety net for code changes and refactoring.

Ensures the proper functioning of the integrated system as a whole.

Usually implemented using testing frameworks like JUnit, NUnit, etc.

Often implemented using frameworks like Selenium, Cypress, or tools for API testing.

Can be executed frequently during the development cycle.

May be executed less frequently due to longer execution times.

Has a narrower scope and focuses on specific code functionality.

Has a broader scope and focuses on the end-to-end behavior of the integrated system.


Unit testing vs integration testing, both have their value, and depending on the project and specific circumstances, we will choose different testing approaches. A good testing tool service provider will offer you the most efficient and fast solutions, and in this regard, you can trust WeTest. With testing based on real devices and cloud-based operations, WeTest brings you cost-saving and secure testing solutions.

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