Handling Flaky Tests in Automation

Table of Contents

• Introduction
• What Makes a Test Flaky?
• Why You Must Address Flaky Tests
• Steps to Handle Flaky Tests
• Preventing Flaky Tests
• Tools to Manage Flaky Tests
• Conclusion

Introduction

Flaky tests—those that sometimes pass and sometimes fail without any changes to the code—are one of the biggest pain points in automation. They undermine the reliability of test suites, waste developer time, and create a lack of trust in automated testing.

In this post, we’ll dive into the causes of flaky tests, strategies to identify and handle them, and best practices to prevent them from occurring in the first place.

What Makes a Test Flaky?

A test is considered flaky when its outcome is inconsistent due to factors unrelated to the application’s code. Common causes include:

1. Timing Issues:

• Tests fail because of slow page loads, delayed API responses, or asynchronous operations.

2. Environment Dependencies:

• Unstable test environments or external services impact test results.

3. Test Data Issues:

• Shared or improperly cleaned test data creates conflicts.

4. Resource Constraints:

• Limited memory, CPU, or bandwidth during test execution.

5. Concurrency Problems:

• Parallel test execution causing race conditions or resource conflicts.

6. Unstable Locators:

• Poorly chosen selectors for UI elements break with minor DOM changes.

Why You Must Address Flaky Tests

• Wasted Time: Debugging intermittent failures drains productivity.
• Delayed Releases: Unreliable tests slow down CI/CD pipelines.
• Loss of Trust: Team members may ignore test failures, reducing the value of automation.

Steps to Handle Flaky Tests

1. Identify Flaky Tests

• Analyze Test Results: Use historical test execution data to spot patterns of inconsistency.
• Build Dashboards: Tools like Jenkins, CircleCI, or GitLab can highlight tests with high failure rates.
• Implement Flaky Test Detection: Some testing frameworks, like Playwright, offer built-in retry mechanisms and reports.

2. Isolate the Cause

• Reproduce the Failure: Run the test multiple times under similar conditions.
• Enable Debugging Tools: Use logs, screenshots, and video recordings to capture detailed information.
• Simplify the Test: Break the test into smaller steps to isolate the failing part.

3. Fix the Underlying Issue

• Timing Issues:

  • Replace static waits with dynamic waits (e.g., waitForSelector, waitForResponse).
  • Ensure proper synchronization between test actions and application states.

• Environment Dependencies:

  • Use mock servers to eliminate dependency on external systems.
  • Standardize test environments using containerization (e.g., Docker).

• Test Data Issues:

  • Generate unique, isolated test data for each test run.
  • Clean up data between tests to prevent conflicts.

• Unstable Locators:

  • Use robust selectors based on unique attributes (e.g., data-test-id).
  • Avoid overly complex or dynamic XPaths.

4. Quarantine Flaky Tests

Temporarily remove flaky tests from the main test suite to avoid blocking pipelines. Quarantined tests can be investigated and fixed separately.

5. Retry Mechanisms

Implement test retries with caution:

• Set limits on retries (e.g., 2-3 attempts).
• Log retries and investigate why they were needed.

Preventing Flaky Tests

1. Adopt Best Practices for Test Design

• Write atomic tests that validate a single functionality.
• Minimize test dependencies to reduce cascading failures.

2. Stabilize the Environment

• Use consistent configurations across environments.
• Leverage infrastructure-as-code tools to standardize setups.

3. Invest in Observability

• Incorporate detailed logging to identify root causes quickly.
• Use monitoring tools to detect resource constraints during execution.

4. Regularly Review and Refactor Tests

• Periodically assess test scripts for inefficiencies.
• Remove outdated or low-value tests from the suite.

Tools to Manage Flaky Tests

• Playwright: Offers retries, screenshots, and tracing for debugging.
• Jest: Includes snapshot testing to detect unexpected changes.
• Allure: Provides detailed test reports for better analysis.
• Build Systems: Jenkins, GitLab, and GitHub Actions support tagging and isolating flaky tests.

Conclusion

Flaky tests are a nuisance, but with the right strategies, they can be tackled effectively. By identifying, isolating, and addressing the root causes of flakiness, you can restore confidence in your automation suite and keep your CI/CD pipelines running smoothly.

What’s your biggest challenge with flaky tests? Share your tips and experiences in the comments below!