The Origin of the Cobra Effect

The term "Cobra Effect" originates from a historical incident during British colonial rule in India. Faced with a significant number of deadly cobras threatening both military and civilian populations, the British government initiated a bounty program, offering 100 rupees for each dead cobra. They anticipated a reduction in the cobra population within months.

However, instead of solving the problem, this initiative backfired. People began to breed cobras for profit, leading to an even greater number of these snakes. Once the authorities recognized that the program was counterproductive and terminated the rewards, the breeders released their cobras, resulting in an increase in the snake population. This phenomenon is now referred to as the "Cobra Effect," symbolizing the unintended consequences of poorly structured incentives.

Programmers and Arbitrary Deadlines

Reflecting on my own experiences, I recall a particular instance from a decade ago while working on a software project. As we approached the end of a sprint, I submitted a final feature just three hours before the deadline. A backlog item remained, but the project manager insisted it must also be completed within the same timeframe. Despite its size, I expressed that finishing it in such a short period was unrealistic.

Unexpectedly, the manager instructed me to take a shortcut: "Create a file, commit it, push it to a new branch, merge it with master, and allow QA to uncover any issues." At that moment, it became clear to me that I could meet arbitrary deadlines by simply delivering additional bugs.

This realization echoed sentiments expressed by Joel Spolsky, who highlighted a similar trend in the Microsoft Word development team, where developers would rely on QA to expedite releases.

«One programmer wrote a simple function to calculate the height of text, opting to wait for bug reports rather than ensuring accuracy.» — Joel Spolsky

Incentives for Developers

Consider the mindset of a developer. They understand that QA will always discover bugs, regardless of severity. If no major issues are present, QA will often find minor ones. Consequently, developers may feel encouraged to rush their work, knowing that the responsibility for identifying issues lies with QA.

Note: If you're seeking metrics to gauge your team's quality improvement, avoid measuring the total number of bugs. Not all bugs carry the same weight or impact; instead, focus on the time taken to resolve them.

This situation can worsen if developers intentionally cut corners, producing a plethora of minor bugs that are challenging to detect. As a result, they might appear to be the fastest and most efficient team members, while the responsibility for these defects falls squarely on QA.

Incentives for the QA Team

On the flip side, how do we assess the effectiveness of the QA team? Common metrics include the severity of bugs found in production, the number of automated tests, and the total count of defects. However, the first metric is often subjective; for instance, some might consider a minor color mismatch a serious issue.

The number of automated tests can be misleading, as having many tests doesn't guarantee comprehensive coverage. Similarly, counting defects can be arbitrary, yet it remains the most commonly used metric.

Typically, QA teams feel a sense of accomplishment when they uncover numerous defects. Imagine receiving a new build and discovering 100 bugs; if only a handful are found later in production, it reflects poorly on your performance. Conversely, if you only find a few during QA, and more emerge post-release, the perception may be entirely different.

This dynamic creates a preference among QA engineers for projects laden with bugs, as their performance is often judged based on the volume of defects they identify.

The Consequences of Perverse Incentives in Software

This sets the stage for what has been termed the "Defect Black Market." When QA serves as a safety net for developers, it inadvertently encourages programmers to generate more bugs, while QA is incentivized to find as many as possible. Thus, an unhealthy cycle of defect creation is established.

«No verbal agreements are needed; both sides understand the benefits of defects, leading to a covert economy of bugs. This issue is rampant in many organizations and can be debilitating.» — Robert C. Martin

Breaking the Cycle

Addressing this issue requires a fundamental shift in how we view the roles of developers and QA. Developers should aim to deliver bug-free code, and QA should not be the last line of defense. If developers rely on QA to clean up their work, they are less likely to prioritize quality in their coding practices.

As John Hunter articulates, «Inspection does not improve or ensure quality; it occurs too late. Quality, good or bad, is already present in the product. You cannot inspect quality into a product.»

To foster an environment where developers produce high-quality code from the outset, the principles of Test-Driven Development (TDD) and shift-left testing must be implemented.

QA should engage with developers before coding begins. By anticipating quality requirements upfront, QA teams can draft test cases that guide development, rather than waiting until after the fact to identify issues.

The New Incentive Structure

Consider the implications of QA writing tests before development occurs. First, it becomes easier to evaluate the QA team's effectiveness. If they can identify all potential edge cases and issues, it indicates a deep understanding of their role. Any defects found post-release would reflect poorly on QA’s foresight.

Second, this collaboration fosters communication between QA and Product teams, allowing for clearer expectations and reducing the likelihood of irrelevant bugs being raised. Finally, developers will have a comprehensive understanding of all use cases prior to coding, leading to fewer misunderstandings and reworks.

Ultimately, developers should assume responsibility for translating human-readable tests into code, ensuring the reliability of their implementations through TDD. When all tests are passed and the code functions correctly, the product is ready for release, minimizing the need for further testing and reducing trivial bugs.

This approach not only eliminates the defect black market but also enhances the quality of the software delivery process.