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In this article, you’ll learn what integration testing is, and how to integrate it into your software testing phases to ensure that every component of your application works in harmony.

Everyone makes mistakes. Even if you’re Richard Stallman, adding the slightest line of code to a program can lead to new bugs. So you must test your applications.

You’ll often hear about unit tests, which allow you to test each class or module of an app individually — see What is Unit Testing?

There is also End-To-End (E2E) testing, which is the opposite of unit testing. They are used to check the validity of a global functionality – technically, we’re talking about testing an endpoint via HTTP, or using front-end technologies to check the behaviors of the final application.

And then there is integration testing, less common but just as important.

What Is Integration Testing?

An integration test is a type of software testing that aims to verify that all the components of an application are working properly, by combining and testing them together.

This ensures that the different parts of the application work well when integrated with each other, and that the interactions between them are coherent. Integration testing generally takes place after unit testing.

A Key Role in Quality Assurance and User Experience

Integration testing is essential to ensure that an application functions correctly as a whole, and to quickly identify any problems that may arise when its various parts are combined. It plays a crucial role in web application quality assurance, helping to deliver a more stable and reliable user experience.

Integration Testing: A Practical Example

Let’s look at a practical example, which will serve as a scenario for the rest of this article. We’re developing an application that manages blog posts, and we want to integrate a dependency that generates newsletters. This dependency is maintained by a partner, so we have no impact on its development.

With unit testing, we check each module individually. We would therefore assume that our application is verified and functional, as is our partner’s module. But several questions arise:

  • Who can certify that the newsletter module works correctly with the articles in my application?
  • How can we guarantee the continuity of compatibility if one of the two parties updates its module?

Integration tests address precisely these issues, since they check that the interfaces of all the parts are respected. It should be noted, however, that integration tests are slightly more complex than unit tests, and the tester needs to be familiar with the functioning of the different modules in order to write the tests.

So It’s a Bit Like End-To-End Testing, Isn’t It?

Yes, but no! With End-to-End testing, we want to go even further. In our scenario, for example, we’d like to check that an e-mail representing our newsletter is delivered successfully to the mailbox of one of our users. We’re going beyond the strict perimeter of our application’s code. Integration testing and E2E testing therefore do not address the same needs.

In addition, E2E tests are often more costly from an infrastructure point of view — having a mailbox, running HTTP requests, etc. — than integration tests. It’s always worth considering whether some E2E tests could be transformed into integration tests, which are de facto much lighter.

What Are the Benefits of Integration Testing?

Adding integration testing to your software testing cycle provides several advantages. Here’s a quick overview.

1. Full Application Coverage

Integration testing aims to test the interactions between the different parts of the application, enabling the detection of problems that could not be identified by unit tests, which test each component individually.

2. Detecting Integration Problems

Integration errors can occur when different parts of the application don’t communicate properly with each other. This is often the case when importing dependencies directly. Integration tests help to detect such problems, and to correct them before roll-out to production.

3. Trust in Updates

Integration tests provide additional assurance when updating, refactoring or adding new functionality. They ensure that changes made do not have a negative impact on system integration.

4. Improving Code Quality

Integration testing encourages the development of modular, well-structured code. By dividing the application into individually testable components, developers are encouraged to write cleaner, more maintainable and more scalable code.

5. Repeatable, Automated Testing

Integration tests are relatively fast and inexpensive infrastructure-wise. This means they can be easily automated, allowing them to be run repeatedly whenever changes are made to the code. This helps to ensure that new features or fixes do not cause regressions in the overall functioning of the program.

6. Living Documentation

Integration testing also serves as living documentation of the interactions between different parts of the code. This makes it easier for new developers joining the project to understand the system.

Integration testing is complementary to unit testing and End-to-End testing, and we can only recommend that you use all of them to improve the quality and stability of your applications.

And if you’d like to find out more about the software security practices of some big players, take a look at our interviews with leboncoin‘s CISO, or Veepee‘s CISO.