Integration Testing vs Unit Testing: Understanding the Differences

Unit testing and integration testing are two of the most important types of software testing. Unit testing is the first testing phase in the software development process and then integration testing is performed. Knowing the role of integration testing vs unit testing along with its key differences will help the team to conduct both these testing types optimally. In this article, you will get to know the differences between unit testing and integration testing.

What is unit testing?

A small piece of code known as a “unit” is tested to know, whether it is working as expected. The objective of unit testing is to ensure that the cost of bug fixes is reduced. This in turn helps in identifying bugs and issues in the early stages of the software development process, as unit testing is the first testing phase of the Software Testing Life Cycle (STLC) process.

Developers are responsible for conducting unit testing. The internal design of the software is worked upon by the unit testing framework. A concise and clear description of the software’s behavior is provided in the form of documentation by the unit testing platform. External dependencies, such as network interfaces or databases are generally mocked up. 

What is integration testing?

It is a testing method wherein the interface between two software modules or units is verified to ensure that it is working as expected. It is performed after unit testing and before system testing. The objective of this testing method is to uncover faults in the interaction that takes place between integrated modules.

The different parts of the system should work cohesively. The overall behavior of integrated modules is tested to know whether it is working as expected or not. The team should know the differences between integration testing vs. unit testing so that both these testing methods can be scaled accordingly.

Use cases for unit testing:

1. Detecting bugs early: Bugs can be detected early through the unit testing platform. The code is being tested by developers as they write it and this means bugs can be detected in the early stages of the software development process.

2. Verifying single component: The functionality of a single component is verified by the unit testing method. Whether it’s a class, a method or a function, unit tests make sure that every part of the code behaves as expected.

Use cases for integration testing:

1. Interface contract verification: The interface contracts between different modules are verified by the integration testing method. It verifies whether a specific module is being correctly used by the output of another module.

2. The interaction between multiple components needs to be verified: The interaction between multiple components is thoroughly verified by the integration testing method. Data communication issues among modules are identified by the integration test method. Knowing the differences between integration testing vs unit testing should also be taken into consideration by the team.  

Differences between unit testing and integration testing:

Unit testing	Integration testing
The unit test suite is run by the CI server at each commit to the check-in or main branch	Integration tests are less often run by the CI server, as the process is basically slow to run
It is easier to write user tests	It is easier to write integration tests
External dependencies (IO, database etc.,) are used for mocking interactions	Real dependencies are used
Unit tests are written by developers	Usually, QA professionals or testers write integration tests
Finding errors is quite busy	Finding errors is quite difficult.

Conclusion: When the team knows the differences between unit testing and integration testing clearly, then they will be able to use both these testing types more productively. For a professional and strategic approach, the team can connect with a leading software testing services company.