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12 February 2024

12 Min. Read

Software testing

Common Types of Bugs in Software Testing

Common Types of Bugs in Software Testing

Key Highlights

In this blog, we cover following key highlights:

  1. Understand bug triage for efficient issue resolution.

  2. Syntax errors are the most common software bugs.

  3. Explore real-world examples of all the types of bugs.

  4. Optimize software performance by identifying and addressing bugs.

Our whitepaper transforms the complexity in microservice testing into a manageable task, ensuring thorough testing that leaves no room for undetected bugs.

Congratulations, you've discovered a new species of bug. What will you name it?

Well, no surprise there!

This is just a part of a tester’s everyday grinding.

It would be weird if someday testers would probably wake up, rub their eyes, and check their screens only to find... nothing out of order.

"Weird," they'd think, sipping their coffee, waiting for the usual chaos to start. But nope, everything's running smoother than a freshly oiled skateboard. No crashes, no weird error messages popping up, nothing. It's like waking up in an alternate reality where everything works perfectly the first time.

So when bugs hold this level of relevance in a tester’s life, then why don’t we write a blog specifically learning about the types of bugs that are known to exist. Joker apart, bugs can seriously stretch the sprint cycle of a product, can leave a product humiliated because of frequent app crashes, and can ultimately put the whole UX down.

With this blog post, we intend to document all the possible types of bugs and will see with example on how big of an impact each bug can create. Let’s get started to uncover the details of all those pesky bugs and let’s get some insights in between on how to smartly act to prevent there existence.

What is a Software Bug?

Imagine you're playing a video game, and suddenly your character falls through the floor and keeps falling into the endless void. That's pretty much a software bug in a nutshell.

A software bug is a glitch, error, or flaw in a software program that causes it to behave in unintended ways. Think of it as when you're following a recipe to the letter, but your cake still comes out looking like a pancake. Something went wrong in the process, and now it's not doing what you expected.

In the coding world, bugs can pop up for a myriad of reasons.

➡️Maybe there's a typo in your code, like misspelling a variable name, or

➡️perhaps there's a logic error where the code doesn't cover all possible scenarios, leading to unexpected results.

Developers write code, and testers play the crucial role of detectives, trying to find these bugs by testing the software in various scenarios. Once a bug is found, it's up to the developers to fix it, ensuring that the software runs smoothly and as intended.

💡 Never let any bug slip-away into production and damage your reputation. Understand how?

Different Types of Bugs in Software Testing

Understanding software bugs is crucial for developers and testers to ensure the development of high-quality applications. Software bugs are flaws or errors in a program that cause it to deliver unexpected results or to behave in unintended ways. These issues can stem from various sources, including mistakes in code, compatibility issues, incorrect assumptions about the environment, or unforeseen user interactions.

Bugs are categorized by their nature (functional, security, performance, etc.), and their severity, which dictates the urgency of their resolution. Identifying and addressing these bugs early in the software development process is vital to prevent potential impacts on the functionality, security, and user experience of the application.

Syntax Bugs: The Typos of the Code World

Imagine you're writing an epic story, but you keep misspelling "the" as "teh." Annoying, right? Syntax bugs are kind of like that, but for programming. They occur when you mistype a part of the code structure, like forgetting a semicolon in JavaScript:

let life = 42
console.log(life) // Oops, where's my semicolon?

Usually, these are easy to fix, once spotted. But until then, they can cause a surprising amount of confusion.

Logical Bugs: When Your Code Loses Its Common Sense

Now, let's say you're programming a smart thermostat. It's supposed to lower the temperature when you're not home. Simple, right? But instead, it cranks up the heat every time you leave, making your return feel like stepping into a sauna.

That's a logical bug – the code does something, but it's not what you intended.


def adjust_temperature(presence):
    if presence == False:
        temperature = 80 # Wait, that's too hot!
        temperature = 68

Logical bugs require a detective's mindset to track down because the code runs without errors—it just makes no logical sense.

Runtime Bugs: The Sneak Attacks

Runtime bugs are like those sneaky ninjas in video games that appear out of nowhere. Your code compiles and starts running smoothly, and then BAM! Something goes wrong while the program is running.

Maybe it's trying to read a file that doesn't exist, or perhaps it's a division by zero that nobody anticipated.

def divide_numbers(x, y):
    return x / y  # What if y is 0? Kaboom!

print(divide_numbers(10, 0))  # Sneak attack!

These bugs can be elusive because they often depend on specific conditions or inputs to appear.

Compatibility Bugs: When Code Can't Get Along

Ever tried to use a PlayStation game in an Xbox? Doesn't work, right? Compatibility bugs are similar. They happen when software works well in one environment (like your shiny new laptop) but crashes and burns in another (like your old desktop from 2009). It could be due to different operating systems, browsers, or even hardware.

Example: A website looks perfect on Chrome but turns into a Picasso painting on Internet Explorer.

Performance Bugs: The Slowpokes

Imagine you're in a race, but you're stuck running in molasses. That's what a performance bug feels like. Your code works, but it's so slow that you could brew a cup of coffee in the time it takes to load a page or process data.

function inefficientLoop() {
    for (let i = 0; i < 1000000; i++) {
        // Some really time-consuming task here

Finding and fixing performance bugs can be a marathon in itself, requiring you to optimize your code to make it run faster.

Performance issues led to the deletion of at least one mobile app for 86% of US users and 82% of UK users.

Security Bugs: The Code's Achilles' Heel

These are the supervillains of the software world. A security bug can expose sensitive information, allow unauthorized access, or enable other nefarious activities. Think of it like leaving your front door wide open with a neon "Welcome" sign for burglars.

Example: A website that doesn't sanitize user input, leading to SQL injection attacks.

SELECT * FROM users WHERE username = 'admin' --' AND password = 'password';

Protecting against security bugs is a top priority, requiring constant vigilance and updates.

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Common Examples of Software Bugs

Software bugs come in all shapes and sizes, and they can pop up from almost anywhere in the code. Here are some common culprits you might encounter:

1. The Classic Off-by-One Error

This bug is like that one friend who always thinks your birthday is a day later than it actually is. In coding, it happens when you loop one time too many or one too few. It's a common sight in loops or when handling arrays.

for i in range(10):  # Suppose we want to access an array of 10 items
    print(array[i+1])  # Oops! This will crash when i is 9 because there's no array[10]

2. Null Pointer Dereference

Imagine asking a friend for a book, but they hand you an empty box instead. That's what happens when your code tries to use a reference or pointer that doesn't actually point to anything valid.

String text = null;
System.out.println(text.length());  // Throws a NullPointerException

3. Memory Leaks

Memory leaks are like clutter in your house. If you keep buying stuff and never throw anything out, eventually, you'll be wading through a sea of junk.

In software, memory leaks happen when the program doesn't properly release memory that it no longer needs, eating up resources over time.

int *ptr = (int*)malloc(sizeof(int));
// Do stuff with ptr
// Oops, forgot to free(ptr), now that memory is lost until the program ends

4. Typos and Syntax Errors

Sometimes, bugs are just simple typos or syntax errors. Maybe you typed if (a = 10) instead of if (a == 10), accidentally assigning a value instead of comparing it. These can be frustrating because they're often hard to spot at a glance.

let score = 100;
if (score = 50) {  // Accidentally assigning 50 to score instead of comparing
    console.log("You scored 50!");  // This will always print

5. Race Conditions

In software, race conditions happen when the outcome depends on the sequence of events, like two threads accessing shared data at the same time without proper synchronization.

# Simplified example
balance = 100

def withdraw(amount):
    global balance
    if balance >= amount:
        balance -= amount  # What if balance changes right here because of another thread?

# If two threads call withdraw() at the same time, they might both check the balance,
# see if it's sufficient, and proceed to withdraw, potentially overdrawing the account.

6. Logic Errors

Sometimes, everything in your code looks right—no syntax errors, no null pointers, but it still doesn't do what you want. This is a logic error, where the issue lies not in the syntax but in the reasoning behind the code.

def calculate_discount(price, discount):
    return price - discount / 100  # forgot to multiply price by discount percentage

Instead of applying the discount percentage to the price, it just subtracts the discount percentage directly from the price, which is not how discounts work.

Strategies for Finding Bugs

1. Rubber Duck Debugging

It might sound quacky, but explaining your code line-by-line to an inanimate object (or a willing listener) can illuminate errors in logic and assumptions you didn't realize you had made.

The process of verbalizing your thought process can help you see your code from a new perspective, often leading to "Aha!" moments where the solution becomes clear. Yes, it's a bit out there, but don't knock it till you've talked to a rubber duck!

2. Version Control Bisection

Git offers a powerful tool called git bisect that helps you find the commit that introduced a bug by using binary search. You start by marking a known bad commit where the bug is present and a good commit where the bug was not yet introduced. Git will then checkout a commit halfway between the two and ask you if the bug is present or not.

This process repeats, narrowing down the range until it pinpoints the exact commit that introduced the bug. This method is a game-changer for tracking down elusive bugs in a codebase with a complex history.

git bisect

3. Profiling and Performance Analysis

Sometimes, bugs manifest as performance issues rather than outright errors. Tools like Valgrind, gprof, or language-specific profilers (like Python's cProfile) can help you identify memory leaks, unnecessary CPU usage, and other inefficiencies.

By analyzing the output, you can often discover underlying bugs causing these performance penalties. For example, an unexpectedly high number of calls to a specific function might indicate a loop that's running more times than it should.

4. Advanced Static Code Analysis

While basic linting catches syntax errors and simple issues, advanced static code analysis tools go deeper. They understand the syntax and semantics of your code, identifying complex bugs such as memory leaks, thread safety issues, and misuse of APIs.

Integrating tools that can provide insights into potential problems before you even run your code, into your CI/CD pipeline can catch bugs early.

💡 Practice shift-left testing and catch all the bugs early-on in the dev cycle.

5. Chaos Engineering

Originally developed by Netflix, chaos engineering involves intentionally introducing faults into your system to test its resilience and discover bugs. This can range from simulating network failures and server crashes to artificially introducing delays in system components.

By observing how your system reacts under stress, you can uncover race conditions, timeout issues, and unexpected behavior under failure conditions. Tools like Chaos Monkey by Netflix are designed to facilitate these experiments in a controlled and safe manner.

6. Pair Programming

Two heads are better than one, especially when it comes to debugging. Pair programming isn't just for writing new code; it's an effective bug-hunting strategy. Having two developers work together on the same problem can lead to faster identification of bugs, as each person brings their own perspective and insights to the table.

This collaboration can lead to more robust solutions and a deeper understanding of the codebase.

7. Fuzz Testing

Fuzz testing or fuzzing involves providing invalid, unexpected, or random data as inputs to a program. The goal is to crash the program or make it behave unexpectedly, thereby uncovering bugs.

Tools like AFL (American Fuzzy Lop) and libFuzzer can automate this process, methodically generating a wide range of inputs to test the robustness of your application. Fuzz testing is particularly useful for discovering vulnerabilities in security-critical software.

Real-World Impact of Software Bugs

Software bugs can have far-reaching consequences, affecting everything from personal data security to the global economy and public safety.

The Heartbleed Bug (2014)

One of the most infamous software bugs in recent history is Heartbleed, a serious vulnerability in the OpenSSL cryptographic software library. This bug left millions of websites' secure communication at risk, potentially exposing users' sensitive data, including passwords, credit card numbers, and personal information, to malicious actors.

What Happened?

Heartbleed was introduced in 2012 but wasn't discovered until April 2014. It was caused by a buffer over-read bug in the OpenSSL software, which is widely used to implement the Internet's Transport Layer Security (TLS) protocol. This vulnerability allowed attackers to read more data from the server's memory than they were supposed to, including SSL private keys, user session cookies, and other potentially sensitive information, without leaving any trace.


  • Massive Scale: Affected approximately 17% (around half a million) of the Internet's secure web servers certified by trusted authorities at the time of discovery.

  • Compromised Security: Enabled attackers to eavesdrop on communications, steal data directly from the services and users, and impersonate services and users.

  • Urgent Response Required: Organizations worldwide scrambled to patch their systems against Heartbleed. This involved updating the vulnerable OpenSSL software, revoking compromised keys, reissuing new encryption certificates, and forcing users to change passwords.

  • Long-Term Repercussions: Despite quick fixes, the long-term impact lingered as not all systems were immediately updated, leaving many vulnerable for an extended period.

Heartbleed was a wake-up call for the tech industry illustrating how a single software bug can have widespread implications, affecting millions of users and businesses globally. It serves as a stark reminder of the importance of software quality assurance, regular security auditing, and the need for continuous vigilance in the digital age.

Preventing Bugs with a Shift-left Test Approach

Leaking bugs into production is not a beautiful sight at all, it costs time, effort and money.

Having a smart testing approach in place is what the agile teams require today. Since most of the errors/bugs are hidden in the code itself, which by no offence, testers can not interpret well. So if a bug is spotted, testers are simply tagging the bug back to its developer to resolve.

So when a developer is responsible for all of it, why to wait for a tester then? That’s where shifting left will be of value. No one understands the code better than who wrote it, so if the dev himself does some sort of testing before giving green signal to pass it on to a QA guy, it would make a whole lot sense if he performs some sort of testing himself.

A static code analyzer or unit testing might be the ideal solution for a dev to help him test his code and know the breaking changes immediately. An ideal approach that works is when all the dependent service owners gets notified if a service owner has made some change in his code, that might or might not break those dependencies.

HyperTest, our no-code tool does just that. The SDK version of it is constantly monitoring the inbound and outbound calls that a service is making to other services. Whenever a dev push any new change to his service, all the dependent service owners get notified immediately via slack, preventing any change to cause failure.

Learn about the detailed approach on how it works here.

Learn about the detailed approach on how it works here.


A deep understanding of software bugs and a robust testing framework are essential for developers and testers to ensure high-quality software delivery. Embracing continuous testing and improvement practices will mitigate the risks associated with software bugs and enhance user experience.

So, next time you encounter a bug, remember: it's just another opportunity to learn, improve, and maybe have a little fun along the way. Happy debugging!

Well, debugging can never be a happy process, as evident clearly. So why wait? Set up HyperTest and let it take all your testing pain away, saving you all the time and effort.

Frequently Asked Questions (FAQs)

1. What Is Bug Triage in Software Testing?

Bug triage in software testing involves prioritizing and categorizing reported bugs. It helps teams decide which issues to address first based on severity, impact, and other factors, ensuring efficient bug resolution.

2. What is the most common type of software bug?

The most common type of software bug is the "syntax error," where code violates the programming language's rules, hindering proper execution. These errors are often detected during the compilation phase of software development.

3. What is an example of a bug?

An example of a bug is a "null pointer exception" in a program, occurring when it tries to access or manipulate data using a null reference, leading to unexpected behavior or crashes.
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