Unit Testing vs. Integration Testing

Unit testing and integration testing are two of the super important testing methods to verify your software. They both come under the umbrella of functional testing and are fundamental procedures to ensure your software quality.

In this article, you’ll learn what unit testing and integration testing are and where they fit into the test pyramid, while you test your project in Agile. You’ll also learn about the notable differences between them to get a thorough understanding, while you implement them for your software.

Unit testing helps verify and validate the functioning of individual testable units or programs in your software. These units are isolated modules/components or functions in a program.

With unit testing, you can ensure that these units function as per the requirements without any defects or bugs. Some notable unit testing tools include TestNG, JUnit, and NUnit.

Integration testing helps confirm that your software modules or units when combined or integrated, run, and function as expected.

With integration testing, you can ensure that there are no defects or bugs when two or more individual units in your software interact with each other through an interface. Once the units pass the unit testing procedures, you integrate them and then conduct integration testing. Postman, SoapUI, and Citrus are some prominent integration testing tools.

Also Read: STLC: Getting Started with Software Testing

Let’s quickly cover the notable differences between unit testing and integration testing:

Mike Cohen came up with the concept of a test pyramid in his book Succeeding with Agile, which divides the testing into organized chunks of testing processes in a granular way. The test pyramid mainly focuses on the Agile methodology or the iterative way to test software.

It also shows the tradeoff between the testing pace and the level of isolation among the most common functional testing methods. Unit testing and integration testing are an integral part of the test pyramid. Here’s a lowdown on it:

• Unit Testing: You start testing your software from the smallest or the most basic unit by writing unit tests for modules/functions/components. Unit tests are usually written by developers since they aim to test your code logic side-by-side as the development goes on. Unit testing is usually faster than other testing methods and is done in isolation. It forms the base of your test pyramid and comprises the most number of tests.
• Integration Testing: When you are done with the unit tests, integration testing comes in next. You confirm if the units that you tested before work as expected when integrated/combined and its interface has no issues whatsoever. Since you test for the correct integration, it’s bound to have dependencies. Integration tests are relatively slower than unit tests and are usually conducted by testers.
• E2E Testing/ System Testing: As you go up the test pyramid, you test your software from start to finish with end-to-end (E2E) testing/system testing, simulating the complete user journey. It’s a time-consuming process and automation tools are usually preferred for it. You generally run E2E/system tests fewer times than the integration tests. Developers and testers usually conduct E2E testing.
• User Acceptance Testing (UAT): Next comes the UAT. Business analysts, stakeholders, and users are your testers here. The user interface and the business logic are looked into while conducting user acceptance testing before your software is prepared to go live.

All the above testing methods are functional testing types. However, there are a few more that come under functional testing, such as regression testing, sanity testing, and smoke testing. Note that these testing procedures are generally conducted after integration testing and before User Acceptance Testing (UAT).

Also Read: Sanity Check: How To’s, Benefits, Features, and More.