The Challenge of Unstable Test Results: Aligning Outcomes with Purpose

Unstable test results; often referred to as "flaky tests", are a well-known challenge in software testing. These are tests that produce inconsistent outcomes, sometimes passing and sometimes failing, without any changes to the underlying code or environment. While "flakiness" is often viewed as a nuisance, it is also a symptom of deeper issues in the testing and development process.

As the article I recently read pointed out, this variability arises most often in areas where testing conditions aren’t fully controlled or where the complexity of the product introduces unexpected variables. While technical parameters like sensitivity in decibels or response times are easier to test consistently, subjective tests -like validating the user experience or unquantifiable product behaviors- often lack clarity and are defined on the fly rather than during the design phase. This reactive approach creates blind spots and contributes to the instability of test outcomes.

Understanding Unstable Tests: A Symptom, Not the Root Cause

Unstable results tend to emerge when:

1. Test conditions are not well-defined: Without clear requirements or controlled environments, tests become non-deterministic.
2. Complexity increases: Issues arise in areas involving runtime race conditions, integration with external dependencies, or complex system interactions.
3. Exploratory testing is underutilized: Tests designed to uncover unexpected behaviors often lack the consistency required for reproducibility, making bugs harder to track.

While it's tempting to reduce instability by avoiding areas prone to variability—such as removing UI tests or minimizing exploratory testing—this approach eliminates opportunities to find critical issues. The most elusive bugs often live in these complex and less-defined areas. Completely eradicating flakiness is not only impossible but also counterproductive; it risks missing the very insights needed to refine the product.

A Common Cause: Undefined Desired Outcomes

One of the biggest contributors to unstable tests in our own context is the lack of clarity around desired outcomes. Without a shared understanding of what success looks like, testing becomes reactive instead of proactive. For example:

• What defines an "intuitive" user experience?
• How should the system behave in edge cases?
• What specific behaviors signal that the product is working as intended versus failing?

Without answers to these questions early in the design phase, tests often rely on improvised metrics, which leads to inconsistent results and misaligned expectations.

A Better Way Forward: Purpose-Driven Testing

To address the root causes of unstable test results and the challenges they represent, we need a more purposeful and proactive approach:

1. Integrate Testing into Product Design Testing shouldn’t be an afterthought. By defining desired outcomes during the product design phase, we can align test objectives with the product’s intent. This ensures that both measurable (technical parameters) and subjective (user experience) outcomes are accounted for.

2. Differentiate Testing Purposes Not all tests serve the same goal, and it’s crucial to distinguish between:

• Verification Tests: Designed to check behavior against well-defined requirements. These should be stabilized with controlled environments to eliminate variability.
• Exploratory Tests: Used to uncover unexpected behaviors and bugs. These tests inherently involve variability and should focus on managing the information derived from inconsistent results.

3. Develop Strategies for Variability

• Use controlled environments and multiple iterations to identify patterns in inconsistent outcomes.
• Treat unstable results as opportunities to investigate root causes, whether they’re technical or related to incomplete requirements.
• Build processes to analyze and act on data from exploratory tests rather than dismissing them as unreliable.

4. Close the Feedback Loop Every instance of instability is feedback. Whether it’s a misaligned requirement, an overlooked edge case, or a design flaw, using this feedback to refine both testing processes and product design ensures continuous improvement.

Conclusion: Unstable Tests as a Path to Better Products

Unstable tests; -or “flaky tests,” as they are sometimes called- are not inherently a bad thing. They highlight areas of complexity, ambiguity, or misalignment that need attention. Instead of avoiding these challenges, organizations like ours need to embrace them with a purpose-driven testing strategy.

By defining outcomes early, differentiating testing goals, and using instability as a source of feedback, we can build a more robust and user-focused development process. This approach not only reduces inefficiencies but also ensures that our products deliver consistent, high-quality experiences.

Unstable tests aren’t just obstacles to overcome; they’re opportunities to understand and improve.