4 Basic Levels of the QA Testing Explained

QA Testing Explained

No application can’t be released without successful testing. Depending on the place in the SDLC and the depth of the tests carried out, there are four main levels of testing: unit, integration, system, and acceptance.

It is important to note that these are exactly the levels of testing, and not stages or types. You can learn more about QA testing in this article, where you will get comprehensive information and a checklist.

The main goal of testing is to make sure that the application operates without malfunctions or failures, however, each of the levels also serves its own purpose.

Unit Testing

This is the simplest level of testing, often carried out directly by the developers before submitting the code to the QA team for testing. This testing aims to determine whether each feature of the application individually works correctly. Simply put: every unit is tested, hence the name of the test. The key advantage of this level is that in this way you can check every part of the code after changes are made and find a bug at an early stage and fix it, instead of going through the entire code afterward.

Integration testing

Once each component has been tested separately, it’s time to test them in a group. An integration test examines the flow from one application module to another and determines how all modules interact with each other. This is a necessary element of a testing strategy because no matter how well each component of the application works in isolation if the integration is not done correctly, failures can occur throughout the whole application.

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When it comes to upgrading an application and adding new features, an integration test is a must. For its implementation, various tools and methods can be used, the choice of which depends on the specific situation.

System Testing

System testing is the most capacious stage at which the application is tested as a complete system. This level consists of a series of functional and non-functional tests that are required to fully explore the application. It can also include tests of design, performance, load, reliability, and security. At this stage, applications are tested on all platforms and gadgets for which it was created, as well as the compliance with the specification and the requirements of the stated goals.

That is, system testing answers not only whether the password entry field is working correctly, but also how quickly the user will get access after entering all the data.

System testing is carried out only by the QA team and is necessary to determine if the application is ready for release.

Acceptance Testing

The final level of testing, which is often called User Acceptance Testing, because users are the main testers. The task of this level is to determine whether the application meets the expectations and requirements of the end-user and globally – the business goals.

As a rule, there are two stages of testing: alpha and beta. Alpha testing is done in a controlled environment, i.e., in addition to a specially selected group of people, it also hosts developers who try to simulate realistic conditions and environments. Beta testing is carried out personally by users on their personal gadgets and in their conditions. According to the standard scheme, they receive the application, use it for a while and send their feedback or fill out a special form based on the results.


For such testing, it is important that the group of testers is as diverse as possible in gender and age, demographics and previous experience of using such applications.

As you can see, such a multi-level testing system ensures high quality, stability and reliability of applications. This testing method is most adapted for agile methodology application development, or while using CI/CD conveyors.

The key principle of this strategy is to start testing as early as possible, as in the case with unit testing. Another important aspect: trust testing to special groups of people – system testing is always carried out by the QA team, and Acceptance testing – by a selected group of users. Only extensive testing can identify the maximum number of bugs (and fix them before launch) and allows you to identify whether the application meets Quality Standards.

 How do you think, all testing levels are required for applications or can some of them be excluded? Please, share your opinion in the comments.



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