In software testing, consistency is critical. When a test passes sometimes and fails at other times without any code changes, it becomes unreliable and difficult to trust. This is known as a flaky test. Flaky tests slow down development, reduce confidence in test results, and can mask real issues in the application.

Understanding flaky tests and learning how to address them is essential for maintaining a stable and efficient testing pipeline.

What Is a Flaky Test?

A flaky test is a test that produces different results across multiple runs, even though the application code has not changed. These tests may fail intermittently due to timing issues, environment inconsistencies, or dependencies on external systems.

Because flaky tests do not provide consistent outcomes, they make it difficult for teams to determine whether a failure represents a real defect or just a testing issue.

Why Flaky Tests Are a Problem

Flaky tests introduce several challenges into the development process:

• Wasted time: Engineers spend time re-running tests instead of fixing real bugs.

• Reduced confidence: Teams begin to ignore test failures.

• Slower CI/CD pipelines: Builds are delayed due to false negatives.

• Hidden defects: Real issues may be overlooked when failures are dismissed.

Over time, flaky tests can severely impact software quality and delivery speed.

Common Causes of Flaky Tests

Flaky tests often occur due to one or more of the following reasons:

Timing and Synchronization Issues
Tests that rely on fixed waits or asynchronous operations may fail inconsistently.

Dependency on External Services
Tests that depend on third-party APIs, databases, or network calls can behave unpredictably.

Shared State and Test Order Dependency
When tests rely on shared data or execution order, results may vary.

Environment Differences
Variations between local, staging, and CI environments can trigger flaky behavior.

How to Identify Flaky Tests

Detecting flaky tests requires careful observation and monitoring:

• Run tests multiple times to check for inconsistent results

• Track failure patterns in CI pipelines

• Analyze logs and timestamps for timing-related issues

• Isolate tests to identify external dependencies

Identifying flaky tests early helps prevent long-term reliability issues.

How to Fix and Prevent Flaky Tests

Reducing flaky tests requires both technical and process improvements:

• Replace fixed waits with dynamic waits or retries

• Mock external dependencies

• Reset test data and environment state between runs

• Avoid shared state across tests

• Improve test isolation and determinism

Addressing the root cause of a flaky test helps restore trust in test automation.

Best Practices to Minimize Flaky Tests

To keep test suites reliable:

• Write deterministic and independent tests

• Run tests in clean, consistent environments

• Monitor flaky test trends over time

• Regularly review and refactor unstable tests

• Treat flaky tests as high-priority issues

Consistency in testing leads to faster and more confident releases.

Conclusion

A flaky test is more than just an annoyance it’s a serious threat to software quality and team productivity. By understanding the causes of flaky tests and applying best practices to prevent them, teams can build reliable test suites and maintain confidence in their CI/CD pipelines.