Software Testing 101: Definition, Types & Everything Else

What is software testing?

Software testing can be defined as a process that evaluates and verifies that a software application or system meets specified requirements and functions as expected. It involves the systematic execution of software components using manual or automated tools to identify defects, errors, or gaps in the software's behavior compared to the intended outcomes. The primary goals of software testing are to ensure quality, reliability, security, and performance, thereby reducing the risk of failures when the software is deployed in a live environment.

Now let’s look at software testing from a different angle.

Think of software testing as a quality detective, searching for hidden flaws and ensuring the program operates as intended. It's like a health check for your software, providing an unbiased assessment of its stability and potential issues.

Software testing simulates real-world use to find bugs, glitches, or anything that could hinder performance, functionality, or user experience. Ideally, testing should be layered like a pyramid, with the most tests happening at the individual building block level (unit tests), followed by tests that ensure different parts work together smoothly (integration tests), and finally, comprehensive tests that mimic real-world usage (system or end-to-end (E2E) tests).

This detective work can involve various methods like unit testing, integration testing, and user acceptance testing. It might even combine manual checks with automated tools. The ultimate goal? To deliver a reliable, secure, and efficient product that satisfies user needs and expectations.

In simpler terms, software testing answers a crucial question: Does the software do what it is supposed to do and what it needs to do?

Why is software testing important?

Software testing acts as a quality guard, identifying issues and ensuring the software functions smoothly. Without it, bugs can cause frustration (a crashing app), financial loss (bank error), or even danger (faulty medical device). By catching these issues early, software testing prevents headaches and safeguards the technology we rely on every day. 

But what if you decide to skip software testing? Well, let’s just say your product could end up housing some pretty nasty bugs. Speaking of which…

Most costly software bugs in history

Software bugs can be expensive—not just in terms of finances but in terms of reputation too. Just look at the impact the CrowdStrike update had on systems worldwide. They made headlines for all the wrong reasons. But they were certainly not the first to wish they’d paid more attention to software testing. Here are some of the biggest financial losses caused by software bugs in history.

The Mariner 1 Spacecraft, 1962

NASA's 1962 mission to Venus, intended to be an unmanned flyby mission, didn't go as planned. The Mariner 1 space probe lost control shortly after launch and began veering off course. Fearing a crash-landing on Earth, NASA engineers were forced to destroy the spacecraft about 290 seconds after launch.

An investigation revealed the cause of the failure to be a critical software bug. A missing hyphen in a single line of code resulted in faulty instructions being sent to the spacecraft. This seemingly minor oversight resulted in a total mission cost of over $18 million (roughly $156 million today). Mariner 1's mission was doomed, however, the mantle of achieving this goal soon fell to Mariner 2, which successfully ventured to Venus and measured its solar wind.

The Mariner 1 mission serves as a reminder of software testing's importance. Even a small error in code can have disastrous consequences.

Costly Heathrow Terminal 5 Opening, 2008

Picture this: you're ready to fly to your dream vacation or go on a crucial business trip, only to be met with flight cancellations and missing luggage. This travel nightmare became a reality for thousands at Heathrow Airport's Terminal 5 grand opening in March 2008, all thanks to faulty software.

The culprit? A brand new baggage handling system. While it functioned perfectly in simulations, it crumbled under real-world use. Conveyor belts malfunctioned, sending suitcases on wild rides or swallowing them whole. Thousands of bags were lost, misplaced, or delivered to incorrect destinations. Adding to the misery, British Airways reported issues with the terminal's wireless network. The result? Over 10 days, a staggering 20,000 bags went missing, and more than 400 flights were grounded, causing over $32​​ million in damages.

This incident serves as a stark reminder of the critical role software plays in modern infrastructure. Even a seemingly minor glitch can cause widespread disruption and significant financial losses.

Software Glitch Costs Knight Capital $440 Million, 2012

A single bad trade can ruin your day, but imagine losing $440 million in just 30 minutes! That's what happened to Knight Capital Group, a major financial firm, thanks to a faulty software update. 

This "upgrade" turned into a nightmare, triggering a buying frenzy that wiped out 75% of their value. Supposed to be a money-making tool, the software glitch sent Knight on a chaotic shopping spree, swallowing up $7 billion in over 150 stocks. 

This digital disaster cost them a staggering $440 million and forced them into a rescue by Goldman Sachs. Sadly, Knight never fully recovered and was acquired by a competitor within a year.

The crash of Airbus A400M

Software errors can have devastating consequences, causing not only significant financial losses, but even tragic loss of life. This is what happened during the crash of an Airbus A400M on May 9, 2015, near Seville, Spain, during a test flight. The aircraft, designated MSN23, was on its first flight and was intended for delivery to the Turkish Air Force. The accident resulted in the deaths of four crew members, while two others were seriously injured.

The cause of the crash was traced back to a software configuration error. During the final assembly process, incorrect data was inadvertently loaded into the aircraft's Electronic Control Units (ECUs). These units manage the engines, and the incorrect data caused three out of the four engines to shut down shortly after takeoff. This resulted in a loss of control, leading to the crash.

This incident highlighted the critical importance of thorough software testing and configuration management in aviation. The crash led to a temporary grounding of the A400M fleet and prompted a meticulous review and correction of software and internal processes to prevent similar tragedies in the future.

Here are some more recent software bugs and tech failures.

The beginning of software testing

Software testing as a formal practice began to take shape in the early days of computing, around the 1950s and 1960s, but it wasn't "invented" by a single individual. The development of software testing evolved alongside the development of programming and computing technologies just after World War II.

One of the earliest mentions of systematic software testing concepts can be attributed to Tom Kilburn, who, on 21 June 1948 at the University of Manchester in England, wrote the first piece of software to run on the Manchester Baby computer. This early software required testing to ensure it worked correctly.

However, the practice of software testing as we understand it today started to formalize in the 1970s with the publication of key literature. Notably, Glenford J. Myers published "The Art of Software Testing" in 1979, which became a seminal book in the field. This book now has been revised and updated by Tom Badgett and Todd M. Thomas with Corey Sandler in 2024. Myers is often credited with laying the foundational principles of software testing that are still relevant today.

Types of software testing

Software testing is generally classified into two primary categories, automated testing and manual testing that can be divided into two distinct levels, each with its own approaches and stages. The detailed diagram below delves into these divisions. 

While it's essential to know what types of software testing there are, it is equally important to understand that the choice of testing method depends on several factors, including the software's complexity, project requirements, and available resources.

Level 1: General software testing categories

At the most fundamental level, software testing can be broadly categorized into manual and automation testing. Depending on the scope and requirements of your project, you may choose to employ manual testing, test automation, or a combination of both. Here is a brief explanation of each:

Manual testing involves human testers executing test cases without the use of automation tools. They rely on their insight to find bugs and ensure the software functions as intended. This type of testing is crucial for understanding the user experience and identifying issues that automated tests might miss.

Automation testing uses specialized tools and scripts to execute test cases automatically, making the process faster and more efficient. It is ideal for repetitive, time-consuming tests and helps ensure consistent testing coverage across various software iterations.

Level 2: Software testing approaches

Your choice between manual and automated testing is just the first step. Next, to achieve a thorough evaluation, you need to understand the most suitable software testing approach for your specific project. Software testing can be broadly categorized into two main areas: functional testing and non-functional testing. Both play a crucial role in ensuring the software's functionality, performance, and overall quality.

Functional testing

Functional testing focuses on whether the software performs its intended functions correctly according to the requirements. Imagine testing all the features of a new calculator app to see if it can add, subtract, multiply, and divide correctly. It can be divided into 4 main testing stages: unit testing, integration testing, smoke testing, and user acceptance testing (UAT). It is important to note that not all functional testing can be automated, for example, UAT is done manually. 

A significant portion of functional testing can be automated using specialized tools and scripting languages. These tools record and playback user actions, allowing testers to efficiently run the same tests repeatedly. This frees up valuable time for testers to focus on more complex scenarios or exploratory testing. Automation also ensures consistency in test execution, reducing the chance of human error that can creep in during manual testing. 

However, it's important to remember that automation isn't a silver bullet. While it excels at repetitive tasks, functional testing also benefits from human expertise, particularly for complex scenarios or testing the user experience from a subjective viewpoint. So, manual and automated testing often work best together for a well-rounded testing strategy.

Non-functional testing

Non-functional testing encompasses all aspects of a system that are not related to its core functionality. This includes performance, security, usability, and compatibility. The primary objective of non-functional testing is to meet customer needs and enhance user-experience. These tests evaluate aspects such as response time, system robustness, and security vulnerabilities.

Non-functional testing is typically conducted using automated tools tailored to the specific type of test. Examples of non-functional tests include load testing, stress testing, and accessibility testing. A common scenario is testing how the software performs under extreme workload conditions, which provides valuable insights into its reliability and efficiency.

This is like testing how fast the app opens, how easy it is to use, how secure it is from hackers, and how well it performs when multiple people use it at the same time.

Level 3: Software testing stages

At Level 3, we explore the various stages that software undergoes during the testing process, depending on the chosen approach—functional or non-functional testing. Using real-world, simple analogies to illustrate each stage, we highlight their significance in ensuring the software's quality and functionality.

Functional testing stages

Unit testing tests individual components or modules of a software application to ensure they function correctly in isolation. Imagine testing the brakes on a car individually before assembling the entire vehicle. 

Integration testing verifies that different modules or components work together as expected within the software system. This is like testing how the brakes, steering wheel, and engine of a car work together.

System testing is a preliminary test to check the basic functionality of the software, ensuring that the critical features work and the build is stable. It's like taking the fully assembled car on a test drive to see if everything works together smoothly.

UAT (User Acceptance Testing) is conducted by end users or stakeholders to ensure the software meets business requirements and is ready for deployment. It is like letting potential customers test drive a car to see if it meets their needs and expectations.

Non-functional testing stages

Performance testing assesses the software's performance under various conditions to ensure it meets speed, responsiveness, and stability requirements. This is like testing the calculator app to see how well it performs when used by millions of people at the same time.

Security testing focuses on identifying and mitigating vulnerabilities in the software that could be exploited by hackers. Imagine testing a banking app to see if a hacker could gain access to your personal information.

Usability testing evaluates how easy and intuitive it is for users to interact with a software application. Imagine you built a new website. Usability testing would involve observing real people as they try to navigate your site, complete tasks, and understand if it's intuitive and user-friendly.

Compatibility testing ensures an application functions as intended across different environments. Imagine testing a phone app to make sure it works on various phone models, operating systems, and screen sizes.

You might be interested in: Usability, UX & Accessibility Testing: Key Differences

Level 4: Software testing types

Having explored the core stages of software testing, let's delve deeper. The final level, level 4, introduces various specific testing types used to ensure software quality at a granular level. We'll continue using real-world analogies to illustrate the purpose and importance of each testing approach.

Sanity testing is a quick check to see if new software is even basically functional after changes have been made. Imagine you're a chef preparing a dish. After adding a new ingredient (code change), you do a quick taste test (sanity test) to see if the dish is spoiled before going through the elaborate process of cooking it (further testing).

Smoke testing is similar to sanity testing, but a bit more thorough. Smoke testing focuses on the most critical functionalities to ensure the build isn't completely broken and can proceed to further testing. It's like a quick health check to make sure the major organs (core functionalities) are functioning well enough before the patient (software) undergoes surgery (more advanced tests).

Accessibility testing ensures that the software can be navigated and used by people with disabilities. Testers consider factors like screen reader compatibility for visually impaired users, keyboard navigation for people who cannot use a mouse, and color contrast to make sure everyone can interact with the software effectively. This includes people with visual impairments, hearing impairments, cognitive disabilities, motor impairments, and more.

Load testing simulates real-world usage by putting the software under increasing pressure with more and more users. It helps identify bottlenecks and ensure the software can handle normal user traffic without slowing down or crashing. Imagine you're managing a theme park. Load testing is like gradually letting more and more people enter the park until it reaches its comfortable capacity. This helps identify bottlenecks in lines, overcrowding in certain areas, or limitations in ride operations.

Stress testing pushes the software beyond its normal capacity, simulating situations like a sudden surge in users or extreme workloads. It helps identify breaking points and ensures the software can handle unexpected spikes in demand without collapsing entirely. Think of it as testing a bridge by overloading it far beyond its intended use to see if it holds or conducting a crash test on a car by driving it at speeds far exceeding normal limits to assess its safety features.

Regression testing is the process of re-running previously successful tests on a modified version of the software to make sure any changes haven't unintentionally broken existing features. This helps catch regressions, which are bugs introduced due to new code that cause previously working functionalities to malfunction. It is like revisiting a recipe you perfected to ensure a new ingredient (code change) hasn't altered the final dish (software functionality). Imagine you've baked a delicious cake countless times. Regression testing is like baking the cake again after substituting a new type of flour (code modification) to confirm it still rises properly and tastes just as good (ensures existing features still work).

Software testing techniques  

Black box testing

Black box testing focuses on functionality from a user's perspective, treating the software as a "black box". It is ideal for ensuring user-expected behavior. Like going for a car ride without looking inside the car.

White box testing

White box testing analyzes the software's internal code, structure, and logic. It is useful for QA engineers to verify code correctness and efficiency. Like a mechanic inspecting a car engine.

Grey box testing

Grey box testing combines elements of both, offering a developer's perspective with some internal knowledge. It is useful when full code access isn't available. Like a mechanic who also uses the car.

Best practices for software testing

Continuous testing. Project teams test each build as it becomes available, allowing software to be validated in real environments earlier in the development cycle. This reduces risks and enhances functionality and design.

User involvement. It's crucial for developers to involve users by asking open-ended questions about the required functionality. This approach ensures the software is developed and tested from the customer’s perspective.

Divide tests into smaller parts: Breaking tests into smaller sections saves time and resources, especially in environments requiring frequent testing. It also enables teams to better analyze tests and their results.

Don't skip regression testing best practices. Regression testing is essential for validating the application and should never be overlooked.

Programmers should avoid writing tests. To prevent bias, it's best practice for programmers to avoid writing test cases. These should be written before the coding phase to ensure objective testing.

Service virtualization. Service virtualization simulates undeveloped or missing systems and services, reducing dependency and allowing testing to start sooner. Teams can modify and reuse configurations to test different scenarios without altering the original environment.

Make communication a core value. Foster open communication between developers, testers, and stakeholders. This ensures everyone is aligned on testing goals and avoids misunderstandings.

Test with the future in mind. Don't just test for current functionality, consider how the software might need to adapt to future changes and technologies.

Report as thoroughly as possible. Document test results in detail by following best bug reporting practices, which include steps to reproduce bugs and suggested fixes. This helps developers pinpoint issues efficiently.

Insist on peer reviews. Encourage developers to have their code reviewed by colleagues. This fresh perspective can help catch errors and improve code quality.

Document the product properly. Create clear and comprehensive documentation, including user manuals and technical specifications. This ensures everyone understands how the software works.

Put security in the testing spotlight. Don't wait until the end to consider security. Integrate security testing, like penetration testing, throughout the development process to identify and fix vulnerabilities early on.

Choose the right testing and management tools. Select tools that automate repetitive tasks, streamline workflows, and provide clear reporting functionalities.

Always aim for code quality. High-quality code is less prone to bugs, making testing more efficient and the software more reliable in the long run.

Involve non-testers in testing efforts: Get feedback from people who will actually use the software. This can help identify usability issues that testers might miss.

Conclusion

Software development is like a big play with lots of different roles to fill parts. Software testers are the amazing backstage crew who make sure everything runs perfectly. They don't just check for mistakes, they also ensure the whole play runs smoothly and is enjoyable for the audience (the users). From checking each tiny detail to running practice scenarios, every step of testing makes the final performance strong and reliable. Remember those times when your favorite app crashed or something went totally wrong? Testing helps prevent those disasters. So next time your tech works perfectly, thank the invisible heroes: the QA engineers. They're the ultimate quality control wizards of the software world.

Looking to improve your software testing efforts? We can help. Contact us to learn more about our software quality assurance services and what we can do to streamline your project.