Difference Between Unit Testing and Integration Testing

You have just identified a problem that people are facing, and you figured out that it can easily be solved by an application. The good news is that you have also built the application with all the necessary features, but it is unable to serve the users and is malfunctioning repeatedly. So, what caused this issue?

The reason behind those malfunctions and crashes is the lack of software testing. Yes, testing every bit of your application is equally or even more important than developing it. You may surely have put a lot of effort into planning, designing, and developing the application as well as all of its features, but you also know that technical things can fail anytime. And, some of the common reasons behind such failures are -

  • The backend server is not capable of handling huge traffic coming from the users.
  • Poorly written code causes server failures due to inefficient running.
  • You have developed the features to work according to the workflow that you have planned, but it is absolutely impossible that every user will use the features in the same workflow.
  • No codebase can ever be bug-free in the first go. Hence, launching a product without debugging its codebase can be your worst nightmare.
    That’s why test-driven development is a highly recommended practice that leads you to update codes with the objective of passing the tests.

There may surely be numerous additional reasons for the malfunctioning of your app, and the best solution to ensure its proper functioning is putting it through in-depth software tests.

Now, talking about software testing surely involves unit testing and integration testing, two of the most important forms of software tests. You must have known about them in detail in our previous articles. Here we are going to find out how they are different from each other.

What Is Unit Testing?

As the name suggests, unit testing is all about ensuring that the smallest software modules which are also called units are working as expected. Units are often small pieces of code so testing them also requires smaller tests. As a complex application can have numerous units, its unit testing phase will also have a similarly high number of unit tests. Hence, unit testing is the largest subset of the testing pyramid.

Now, as you know that the more you proceed through the step-by-step software testing process, the cost of fixing the detected bugs becomes higher. So, to avoid those high costs, unit tests are performed during the first phase of the testing process. As a result, it becomes easier to detect and fix all the bugs in every small unit of the application while maintaining an affordable quality assurance budget.

Unit testing was initially done by developers but, with the exponential growth in the number of applications as well as the testing workload, dedicated QA professionals are given the responsibility for performing these tests along with all other forms of testing.

Modern agile practices suggest that QA engineers should be completely involved in the development process from the beginning. That way they can focus on quality improvement measures more efficiently, and figure out points to improve.

However, as the world is currently accepting automation testing to experience maximum performance and ease of operation, highly efficient test automation tools like Preflight allow you to run unit tests within a few seconds.

What Is Integration Testing?

Integration tests are responsible for checking the integration between two software modules or units. The integration testing phase comes next to the unit testing part of the testing process. So, after the unit tests have ensured that every individual unit is bug-free, the integration tests verify that the interface between the two units is working as expected.

These tests are highly important because multiple individual software modules can collaboratively perform a task only when the interconnections among them are performing properly. Hence, these tests are not always about involving only two units in one test. Integration tests may involve multiple units or even the whole application at a time. You can get to know all about its operational details in the article “An Introductory Guide To Integration Testing | Types, Checkpoints and Process”.

Differences Between Unit Testing and Integration Testing

Now, it’s time to check out the differences between these two important forms of testing.

Unit Testing

Integration Testing

These tests check for bugs in every smallest software module which is also called a unit.

These tests ensure that the interface between two units is functioning properly.

Though these tests are normally performed in the first phase of the testing process, they can be performed at any point in the entire process.

These tests are mostly performed after unit testing and before the overall system testing.

It takes significantly less time to write and run these tests.

Writing and especially, running these tests is a comparatively time-consuming process.

Unit testing is a kind of white-box testing.

Integration testing is a kind of black-box testing.

Normally, software developers are responsible for running these tests.

These tests usually have dedicated teams of testers to run them.

Unit tests need the testing team to know the internal design of the software.

Integration tests do not need the testing team to know the internal design of the software.

Unit tests have a very small scope that makes them capable of detecting only the errors in individual units. They cannot detect integration errors or any other issues in the system.

The primary objective of integration tests is identifying the errors in the integrations between different modules of the system.

These tests do not have any external dependencies. And, if required, external dependencies are mocked or stubbed out.

These tests need to interact with external dependencies such as databases, hardware, etc.

Unit tests are quite simple.

Integration tests are comparatively complex.

Unit tests are less costly.

Integration tests are more costly.

Unit tests start with module specifications.

Integration tests start with interface specifications.

Maintaining unit tests is cheaper.

Maintaining integration tests is comparatively expensive.

These tests are focused on the behavior of single modules.

These tests are focused on the integration among modules.

The outcome of unit tests is a detailed visibility of the code.

The outcome of integration tests is a detailed visibility of the integration structure.

Similarities Between Unit Testing and Integration Testing

From the above-mentioned differences between unit testing and integration testing, you must have understood why each of them is unique in itself. But, you must know that being two highly crucial parts of the software testing process, they share some similarities too. So, let’s check them out.

The primary similarity between these two forms of testing is that both of them hold almost the same importance for the correctness of an application’s codebase. If you want to launch a properly working application, neither of them can be ignored, nor can any one of them be prioritized more than the other one.

Both unit testing and integration testing are two unavoidable aspects of functional testing, and in traditional testing methods, they require complex coding to be successful.

However, in the modern era, efficient codeless testing tools like Preflight allow anyone to easily perform unit tests, integration tests along with every other form of tests irrespective of his/her coding knowledge. So, if you want to perform these tests and feel insecure about your coding skills, codeless test automation tools are the perfect solution for you.


Both Unit testing and Integration testing are extremely important for the smooth running of a tech product, and the objective of any one out of them will never get fulfilled without the perfect running of the other one. Besides making you aware of the differences between these two forms of testing, this article also provides you with an idea of why these test forms are so important for the successful launch & running of your application.

Software testing is absolutely unavoidable, and the most efficient way to reach its heights is by automating it. That’s why modern agile methodologies highly prefer the usage of advanced AI-based test automation tools like Preflight. The super powerful AI features of this tool can do wonders for your testing process. So, don’t wait more to get a glimpse of such a magical testing experience for free.

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