Psychological Biases Every Tester Should Be Aware Of

In the world of testing, we believe that we are objective and methodical, but in reality, our brains are subject to cognitive biases that affect the way we conduct tests, search for bugs, and analyze results. Recognizing these biases is a key step in becoming better testers.

Bug Blindness Effect

What is it?

After testing the same screen or process repeatedly, the brain gets used to it and stops noticing details. We see what we expect to see, not what is actually there.

How to avoid it?

• Take a break and refresh your mind or check other areas.

• Have someone else test the area you’re already familiar with.

• Change your approach (use Exploratory Testing rather than sticking to fixed scripts).

Confirmation

What is it?

Look for information that confirms what we already believe and ignore information that contradicts it. In testing, this happens when testers examine a system based on how it is "supposed" to work and don’t look for ways it might break.

How to avoid it?

• Try to falsify your assumptions instead of confirming them.

• Ask other testers to approach the system from a distinct perspective.

• See how the system reacts to unexpected input.

Illusion of Completeness

What is it?

The feeling that if we've covered all the planned test scenarios, the system is "bug-free." In reality, there are always gaps that can be missed.

How to avoid it?

• Remember that 100% coverage doesn’t exist—there is always something to test.

• Analyze previous failures and check if there are areas that weren't tested enough, including specification documents.

• Perform Exploratory Testing beyond the usual script boundaries.

Curse of Knowledge

What is it?

When you are familiar with the system, it becomes difficult to imagine how a new user would interact with it. That’s why it’s easy to miss issues that new users will encounter right away.

How to avoid it?

• Ask someone unfamiliar with the system to test it (or even perform tests as if you were a new user).

• Check with support staff to see what problems users actually have.

• Try performing tasks without using prior knowledge, such as relying only on documentation.

Anchoring

What is it?

Lean on the first piece of information we encounter and ignore other details. For example, if a developer tells us the issue is "probably in the database," we may start checking there only, rather than thinking of other possibilities.

How to avoid it?

• Don’t start with an assumed solution, first gather as much data as possible.

• Explore other directions.

• Share your findings with other testers to gain new perspectives.

Optimism

What is it?

The believe that everything "will work fine" and to plan tests assuming normal behavior. In reality, users will always find ways to use the system in unexpected ways.

How to avoid it?

• Build scenarios that simulate user errors.

• Test how the system responds to incorrect input, weak networks and corrupted files.

• Don’t just test the "happy flow"—test what happens when everything breaks.

Why is this important for QA?

Understanding these psychological biases can significantly improve the quality of work for any tester.

The more we recognize our biases, the better we can focus on finding issues from all angles, not just based on fixed patterns.

This isn’t just about improving personal testing skills, but also about improving the overall work process within a team.

By ensuring diverse testing methods and creative thinking, we can avoid the traps of cognitive biases and identify issues that might otherwise go unnoticed.

All of this contributes to a better product, ensuring that the system is stable, and reliable—while maintaining a more objective and focused approach to testing.