Software Testing

A Complete Guide to the Different Levels of Software Testing

Did you know that the average company spends more than $340,000 on software-as-a-service (SaaS) applications? When companies are spending that much money on software applications, they expect the software to work perfectly every time. But, the only way that can happen is through extensive testing.

In fact, there are even certain levels of software testing that developers follow to make sure they’re putting the best possible product on the market.

So, what exactly are the four levels of software testing? You’ve come to the right place for answers. Keep reading this guide to learn more about the stages of software testing so you have a better understanding of how it all works.

Level 1: Unit Testing

The first of the software testing levels is unit testing, where developers test the individual parts of the software. A unit, or component, is essentially the smallest functional part of a piece of software. While it has to work in conjunction with other units to function properly, developers can still test each unit separately.

This is important because it allows the developers to test very small pieces of code individually. This helps to identify potential issues on a small scale. From there, they can make incremental updates, without having to worry that the changes will affect other aspects of the software.

Unit testing is key because it identifies issues in the internal workings of the software as a whole, before testing more complex components of the software. This makes it easier to troubleshoot where exactly the code issue is, so it’s easier to come up with an appropriate fix.

Of course, even when testing small pieces of code during unit testing, there’s a potential for uncovering major bugs. So, testers must be extremely detailed even during this early stage of testing.

Level 2: Integration Testing

After unit testing is complete, it’s time to move onto the next level, which is integration testing. During this phase, developers put together a group of interacting units and test how they work together. Why is this important? Well, since the different pieces of code were likely written by different developers, it helps to ensure that they work the way they should.

Specifically, testers are checking to make sure that:

  • Different modules can communicate with each other
  • The application works well on different platforms
  • Security measures work correctly between different systems

There are generally four different approaches that testers take during this level.

Bottom-up Integration Testing

As its name suggests, this approach starts at the bottom and works up. So, developers will test low-level code modules first, identifying any issues. If everything looks good, then they’ll continue working their way up. They’ll then test higher-level modules to ensure that everything continues working properly every step of the way.

Top-Down Integration Testing

Top-down integration testing works in the opposite way. Essentially, developers using this approach will simulate the expected behavior of low-level modules that haven’t yet been integrated. Ideally, this will give the same type of output as the actual product will, so it’s a fairly accurate testing scenario.

Big Bang Integration Testing

During this approach, all the elements in a test scenario are tested at the same time. Developers tend to use this approach for small applications. In those cases, it’s usually not necessary to perform bottom-up or top-down testing.

Mixed Integration Testing

Also known as sandwiched integration testing, this approach doesn’t give priority to either high-level or low-level modules. Instead, developers test modules as they are available, instead of waiting to test in a specific order.

Level 3: System Testing

After unit testing and integration testing, developers will move on to system testing. During this stage, they test all of the code together in a testing environment that’s similar to the final deployment environment.

The goal during this testing phase is to make sure the software has all the initial requirements working properly. By doing unit and integration testing first, the testers should have been able to eliminate the majority of the bugs in the code, so by the time they’re ready for system testing, ideally, there won’t be any major defects.

Generally, testers will take two approaches to system testing.

Requirements-Based System Testing

Using a requirements-based approach, quality assurance testers test based on the software’s requirements. So, they’ll write out detailed test cases for each requirement. Then, they’ll perform the tests to make sure the software meets each one.

Use Care-Based System Testing

In this approach, testers focus on how end users will use the software instead of requirements. In this case, they’ll write out specific test cases for each use case, sometimes with multiple scenarios for each use case. From there, they’ll perform the tests to identify any potential issues.

Level 4: Acceptance Testing

The final level of software testing is acceptance testing. This is a more formal testing phase, where the primary goal is to test to make sure the software is in compliance with all the system requirements.

At this point, the client—not the developers or testers—will test the software for themselves to make sure it meets the needs of their business. Sometimes, the client will opt to use a third-party testing company instead, so there’s an unbiased party testing the final software.

If the client has updates, the software goes back to the developers for updates. However, if the client approves the software after the acceptance testing phase, then it’s ready for release.

To learn even more about software testing, check out

Understanding the Four Levels of Software Testing

Now that you’ve read this guide to the four levels of software testing, you should have a better idea of all the work that goes on behind the scenes before the software is released. The next time you find yourself using a piece of software, think about all the testing that had to happen to get it to where you can actually use it!

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About Ambika Taylor

Myself Ambika Taylor. I am admin of For any business query, you can contact me at [email protected]