It may be hard to believe, but there was a time when people—whether before, during, or after a purchase—didn’t test whether a product worked; they simply waited for it to fail. This practice was also quite common in the early days of the software industry, when testing practices were virtually nonexistent. This situation began to change in the 1950s, when the history of testing in application development began.

Over the past seventy years, testing has evolved significantly. Today, it is fully integrated into the routine of developing digital products or modernizing applications. As software development has scaled up and become more complex—largely driven by cloud computing—there has been an exponential increase in the volume of testing.

However, it wasn’t just the quantity that changed. The perspective and purpose of testing also evolved, especially as the 1970s gave way to the 1980s. Stay with us in this article to learn a little more about the history of testing and understand the role it plays today in application development.

When software testing first emerged

The earliest discussions in the technical and scientific literature on testing come from Alan Turing. In articles published at the turn of the 1940s and 1950s, the “father of computing” discusses the use of assertions to verify the correctness of algorithms.

The texts fall within the period that David Gelperin and Bill Hetzel classify as the “purification-oriented phase,” the first of five periods in the history of testing. According to the authors, these phases are:

We can classify the first two periods as the “prehistory” of testing. This is because 1979 was the year the book*The Art of Software Testing*—in Portuguese, *A Arte de Testes em Software*—by computer scientist Glenford Myers was published. The book is the industry’s most significant milestone on the subject, so much so that it remains a standard reference on quality management in software development to this day.

In the early stages of the history of testing—the debugging-oriented phase—tests were performed only when the machine encountered an error. Testing was the debugging activity itself. In fact, in much of the technical literature of the time, the terms “debugging” and“testing”were often used interchangeably.

It’s worth remembering that, during this period in history, computers and software were not interchangeable; when a company purchased a machine, it came with its own operating system. This peculiarity was also evident in testing practices: testing focused much more on hardware than on software. Software issues were deprioritized—and often ignored—in light of concerns about hardware reliability.

In the second phase—the phase focused on demonstration, testing, and debugging— these activities came to be viewed as distinct. This distinction is made clear in the book *Digital Computer Programming* by Dan McCracken. Based on this approach, the goal of testing was not to fix a machine when it encountered errors, but rather to demonstrate that the program ran and solved the proposed problems. In other words, that the software met the requirements.

This more professional and meticulous approach to testing became necessary as applications evolved, both in terms of complexity and cost. With more software on the market, the number of bugs and problems multiplied. This increased the financial risk that software failures could cause, leading to higher quality standards and greater investment in testing activities.

History of Testing: From Guidance to Destruction to Preventive Action

In 1979, “The Art of Software Testing” was published, marking a major milestone in the field. Its significance stems from the fact that it proposes both a new logic and a new objective for the testing process.

In the “destruction-oriented” phase, the desired end result was the same as in the previous phase: software that works and meets the requirements. But Myers proposes a new, holistic way to achieve this goal: to verify all the scenarios that could lead to an error. Software testing should not be about checking what is working, but rather about running a program with the intention of finding errors.

It is thanks to “The Art of Software Testing” that testing has come to serve its current purpose: prevention. By shifting the focus from demonstration to the detection of potential problems, the activity now aims at total quality, making it possible to verify the conformance of applications upon their completion.

The two subsequent phases—both the evolution-oriented and prevention-oriented phases—are extensions of the destruction-oriented phase. They do not alter the principle; they merely add objectives to the testing activity.

In the evolution-oriented phase, testing becomes integrated with review and analysis to promote the product’s evolution throughout the application’s life cycle. In other words, the purpose of testing remains to find errors. However, the information gathered from these errors now serves as the starting point for planning system improvements.

Finally, the current phase—which is focused on prevention—can be summarized by the phrase“quality as a service.” Testing does not take place once the software is complete, but rather throughout the entire development cycle, starting with the concept phase. Testing is conducted in parallel with the creation of the application, at every stage of the project.

It is within the context of this approach that the development methodologies currently widely used in the market have emerged: test-driven development —used for unit testing —behavior-driven development, and acceptance test-driven development.

Inmetrics' role in this story

Inmetrics’ entire history is closely tied to testing. We started out as a company dedicated to improving the quality and performance of applications. As part of our DNA, this is reflected in everything we do. It’s no surprise, then, that we’re a leading company in Continuous Testing on the ISG Provider Lens Next-Gen ADM Services Brazil 2022 report.

If you need to develop truly robust applications that perform flawlessly, with the entire environment monitored and corrected almost instantly, click here, talk to our team of experts, and learn about all our solutions!

Frequently Asked Questions About the History of Software Testing

1. What are the 5 phases in the history of software testing?
   They are: debugging-oriented (until 1956), demonstration-oriented (1957–1978), destruction-oriented (1979–1982), evolution-oriented (1983–1987), and prevention-oriented (from 1988 onward), according to the classification by David Gelperin and Bill Hetzel.
2. Which book marked a turning point in the history of software testing?
   *The Art of Software Testing* by Glenford Myers, published in 1979. The book proposed that the goal of testing was to actively find errors, rather than merely demonstrating that the software worked—a shift that gave rise to the current focus on prevention.
3. What is the difference between testing and debugging?
   In the early decades of computing, the two terms were used interchangeably. Beginning with the demonstration-oriented phase (1957–1978), they came to be treated as distinct activities: debugging corrects an identified error, while testing is intended to find it.
4. How does software testing work today?
   In the current phase, which is focused on prevention, testing occurs in parallel with all stages of development—not just at the end—following the “quality as a service” approach. This has given rise to practices such as test-driven development, behavior-driven development, and Continuous Testing.