No tests, no success: an overview of the most important software test types

Imagine you build a car and test every single component, e.g. brakes, indicators and sensors, before you install it. This is exactly what unit tests do with code: They test small, isolated parts such as functions or methods to see if they work correctly. This is quick, inexpensive and prevents problems before they hit the road.
If only the bulb in the indicators is changed later, you can check immediately whether the rest still works, instead of finding out on the next test drive that the brake lights no longer light up.

Just because every switch and every indicator light works individually does not mean that the whole car will drive. Integration tests check whether different parts of the software work well together. For example, whether the app communicates properly with the database or controls external services correctly – just like the blinker lever switches the indicator light on and off.

Here, the entire software is tested under realistic conditions. Does everything run smoothly when real data flows and real hardware is involved? System tests simulate everyday life as closely as possible.

In the end, only one thing counts: are the users happy? Acceptance tests simulate typical application scenarios and check whether the software really delivers what everyone imagined. These tests often decide whether a project is accepted or needs to be revised again.

Do you know the feeling when you are repairing something and accidentally break something else? This happens all the time in software engineering. Regression tests ensure that everything works exactly as it did before after every change.

Sometimes you find the most interesting bugs by simply clicking wildly through the software and seeing what happens. Exploratory tests do not follow a fixed plan, but rely on the experience and intuition of the testers. Problems are often discovered in this way that automated tests would have overlooked.

Like a proofreader checking a text for spelling mistakes, static analysis looks at the code without executing it. It finds security vulnerabilities, potential sources of errors or places where good programming practices are being violated.

Functional tests check the “what” – does the software do what it is supposed to do? Non-functional tests look at the “how” – is it fast enough, secure enough, can it cope with many users at the same time?

If you’re now thinking “Wow, that’s a lot” – don’t worry, you don’t have to introduce all test types at once. But some are really essential:

Unit and integration tests are like a safety net when programming. They let you know immediately if something goes wrong and help to ensure that errors are not discovered later in the engineering process, when they are much more expensive to fix.

Regression tests are your protection against nasty surprises. They ensure that updates do not secretly break other functions.

System and acceptance tests are your quality check before publication. They guarantee that you end up with a usable product that users are happy with.

Admittedly, all these tests take time and effort. But they pay off:

Problems are found early, when they are still easy and cheap to solve. The code becomes more stable and is easier to develop further. With automated tests, new versions can be released more quickly because you can be sure that nothing important is broken. And in the end, you get software that really does what it is supposed to – both technically and from the user’s point of view.

Especially in a world where product cycles are constantly shortening with continuous delivery, it is crucial to be able to roll out even small changes without a great deal of manual testing. And it is precisely this security that tests offer.

For us, unit tests are an indispensable standard part of every project. We don’t write them for the customer or the project manager – we write them for ourselves. Because our software is not a static bunker, but is constantly being developed, improved, supplemented and adapted.

Unit tests give our software engineers the security they need to make such changes without fear of everything suddenly falling apart “at the other end”.

Integration tests for business-critical processes are also an integral part of our projects. In addition, we actively support the planning and implementation of customized test strategies – individually tailored to the requirements, processes and standards of our customers.

Professional software engineering without structured tests? That’s like driving a car without brakes – theoretically possible, but not a good idea. Unit tests, integration tests, system tests and acceptance tests are the foundation for software that not only works, but is also reliable, maintainable and user-friendly.

They have long been standard in modern engineering teams. Not because they are fun (even if some engineers claim that), but because they are simply necessary for good software.