How many times have you read your code and overlooked the obvious? It’s probably happened a lot because there are a number of common cognitive biases that lead even the best developers to miss bugs in their own code, even after multiple personal reviews. Why do these blind spots occur, how does mental fatigue and familiarity impact debugging, and – most importantly – how can programmers develop practical techniques to improve error detection? 

One of the primary reasons developers overlook bugs is due to cognitive biases, which are systematic patterns of deviation from norms or rationality in judgment. When it comes to coding, one of the most prevalent biases is the “confirmation bias.” This occurs when developers subconsciously look for evidence that supports their existing beliefs and ignore evidence that contradicts them. For instance, if you believe your code is flawless, you might overlook obvious errors because you’re not actively searching for them.

Another significant bias is “familiarity bias.” When you write and review your own code, you become overly familiar with it, which can cause you to see what you expect to see, rather than what is actually there. It’s like reading a sentence with a missing word; your brain fills in the gap, and you don’t notice the omission.

Mental fatigue also plays a crucial role in overlooking bugs. Coding is a mentally demanding task, and after hours of being immersed in your code, your brain’s ability to spot errors diminishes. This is why it’s often recommended to take regular breaks and return to your code with fresh eyes. A fresh perspective can help you spot mistakes that you previously missed.

To combat these biases and improve error detection, there are several practical techniques you can employ. One effective method is to use peer code reviews. Having another set of eyes on your code can help identify issues that you might have missed. Paired programming, where two developers work together on the same code, can also be beneficial. This collaborative approach ensures that both developers are actively engaged in the coding process and scrutinizing each other’s code, thereby reducing the likelihood of overlooked bugs.

Automated test scripts leveraging either test driven development or behavior driven development is another approach to catching errors early in the development cycle. Often called ‘shift left’ testing, creating a suite of test scripts based off of a comprehensive test plan can help catch errors early in the development process. These test scripts can be run automatically within your devops tools stack, ensuring that your code behaves as expected throughout the development cycle and even after changes are made.

While your brain is a powerful tool, it’s not always your best debugger. Cognitive biases, familiarity, and mental fatigue can all contribute to overlooked bugs. By being aware of these factors and employing practical techniques like code reviews, paired programming, and automated test scripts, you can improve your error detection and write more reliable code. Remember, sometimes the best way to find bugs in your code is to step back and let someone else take a look.