What is a Flaky Test? (Characteristics, Causes, Resolution)
By Shormistha Chatterjee, Community Contributor - September 3, 2023
The flaky test is a major issue software testers and developers encounter during SDLC. These tests refer to testing that generates inconsistent outcomes, failing or passing unpredictably, without any modifications to the code under testing. Flaky tests can be annoying and, at the same time, time-consuming as they result in unreliable test results and less productivity.
This guide will briefly introduce flaky tests, exploring their traits, what causes flaky tests, and effective solutions to resolve their impact.
What is a Flaky Test?
A flaky test is an automated test that validates inconsistent behavior, generating distinct results when implemented multiple times on similar functionality. Such tests are known for their unpredictability, as they can fail or pass intermittently without any alterations to the code or the application under test.
The unreliability of these tests can significantly disrupt the complete test process, resulting in wasted effort, time and decreasing trust in the consistency of the test results. Besides, these tests can be a source of frustration for software developers as their failures don’t always signify the existence of an actual bug.
- In fact, in a software pipeline where regression tests are implemented before every single code commit, the presence of flaky tests causes delays as they can falsely appear to be related to one or more code changes.
- This circumstance consumes developer time and forms unnecessary hindrances in the development workflow.
In the given figure, there is a flaky test from the PySyft project. This test comprises an assertion (mentioned) on line 11 that verifies an operation’s completion time.
Characteristics of Flaky Tests
These tests demonstrate various characteristics that distinguish them from reliable testing.
Let’s take a glance at some of the critical traits of flaky tests:
- Inconsistent Behavior and unpredictable results: These tests are well-known for their inconsistent and unpredictable results. Contrasting reliable tests that produce consistent results, these tests generate varying results when implemented multiple times on similar functionality. This uncertainty makes it perplexing to rely on the outcomes of flaky tests and undermines confidence in the test process.
- Unpredictability nature: Flaky tests exhibit unpredictable nature. These tests can pass or fail, apparently at random, without any strong reason or pattern—the lack of a clear pattern or reason challenges software testers or teams. The unpredictability of these tests weakens the confidence in the accuracy and consistency of the test process.
- Non-Deterministic Implementation: These tests exhibit a non-deterministic execution, meaning they can be influenced by external factors like the order of execution, timing concerns, race conditions, etc., that result in inconsistency and variability in the test outcomes.
- False Positives/Negatives: These tests can produce false positives, representing the presence of a bug when there is none, or false negatives, failing to detect actual issues. This inconsistency undermines the reliability of the test suite.
What Causes Flaky Tests?
Myriad factors can cause flaky tests; understanding these causes is critical for smartly addressing flakiness and enhancing the reliability of test automation.
Some of the most common causes of flaky tests include:
- Poorly written tests: One of the most common reasons for these tests is poorly written tests. Testing can produce inconsistent outcomes and flakiness When it isn’t designed or executed appropriately.
- Timing & Synchronization Issues: Flaky tests also happen when there is a need for proper synchronization between test phases as well as timing dependencies. Such issues can cause inconsistent outcomes, particularly in scenarios relating to concurrent or parallel execution.
- Environmental Factors: These tests can be caused by environmental factors like network connectivity issues, fluctuations in system resources (memory, CPU), or dependencies on APIs or third-party services.
- Unstable Test Environment: These tests can result from an uneven test environment, counting inadequate configuration, unreliable test infrastructure, or partial test setup variations in the environment can affect test outcomes.
- Async waits: One of the key factors that can also contribute to flaky tests is the inappropriate handling of asynchronous waits and operations. Asynchronous operations, like network requests or User Interface updates, might introduce race conditions and timing problems if mishandled.
- Concurrency: Flakiness also happens when a tester/ developer makes an inappropriate statement about the order in which the varied threads are applying operations.
Read More: How to avoid Flaky Tests?
Impact of Flaky Tests
Flaky Tests considerably influence QA/ software tests because of their non-deterministic and unpredictable outcomes, affecting the test procedure’s consistency.
Let us look at some impacts flaky tests can have on SDLC:
- Extra Debugging Efforts: These tests necessitate extra effort and time to detect the root cause of failures. Test failures that aren’t because of real bugs can result in wasted debugging efforts, as software developers might spend time scrutinizing false positives or attempting to mitigate issues that don’t exist.
- Test Stability: These tests can influence the steadiness of the test suite. If a test is flaky, it can occasionally exhibit failures while passing on the next runs. This discrepancy can cause tests to be disabled or removed, which can decrease the overall efficiency of the test procedure.
- Decreased Test Coverage: Flaky tests can cause a reduction in the entire test coverage of the codebase. In case, if developers lose trust in any test because of its unreliable behavior, they might choose to remove or skip it from the test suite.
- Increased Maintenance Expenses: These tests can increase maintenance expenses for a test suite. The intermittent failures might necessitate extra effort to keep them reliable and up-to-date. Developers may require to invest additional time to maintain the test suite as a whole to address concerns linked to flakiness.
- Low Confidence in Test Outcomes: These tests undermine the confidence in the accuracy and consistency of the test outcomes. Unpredictable Test failures make it perplexing to trust the validity of the test results. This can cause doubts about the efficiency of the testing process and the overall software quality being tested.
- Decreased Efficiency: These tests can have a negative influence on the effectiveness of the testing process. When tests fail intermittently because of flakiness, it can cause unnecessary rework and retests. This leads to wasted effort and time for the QA team, reducing productivity.
- Negative Impact on Test Automation: Flaky tests can erode trust in automated tests as an effective and reliable tests approach. This can cause skepticism toward test automation practices and hinder the acceptance of automated tests within the organization. To mitigate the negative influence of flaky tests on test automation, addressing the main causes of flakiness is vital.
With Automate TurboScale (a scalable and reliable test automation infrastructure), you can easily execute automated tests written in varied frameworks across distinct browsers and a series of browser versions.
How to resolve Test Flakiness?
To lessen the impact of flakiness and confirm a test suite free from flaky tests, it is vital to adopt proactive maintenance practices and execute effective strategies.
By following these strategies, testing teams can enhance the stability of their test suites:
- Analyze Test Logs & Failure Patterns: Thoroughly analyze and scrutinize the test logs & failure patterns to determine any inconsistencies or recurrent issues. Look for the failure patterns, such as test data, precise environments, or timing-centric issues. This scrutiny can help pinpoint potential reasons for flakiness.
- Monitor Test Implementation History & Trends: Keep track of the test implementation history & trends to detect tests that constantly exhibit flakiness. Seek for tests that recurrently fail or release inconsistent outcomes amid multiple test runs. Observing the trends can assist in prioritizing the resolution of flaky tests.
- Leverage Smart Tools for Flaky Test Detection: Use dedicated/ smart frameworks or tools that precisely address flaky test detection. Such tools can deliver insights and study the consistency and stability of tests. They can help recognize tests with higher flakiness rates and give valuable metrics for further exploration or examination.
- Report & Track Flaky Tests: Execute a system to report and track flaky tests. Document the detected flaky tests, comprising the particular failures, related environments, and any related details. This documentation serves as a reference to rapidly track the progress of solving flaky tests and guarantees transparency within the tests team.
- Enhance flaky test detection, and gain comprehensive visibility into your test outcomes—all in one centralized location.
- Fix faster with Smart Failure Analysis, which learns from your testing and identifies the causes of test failures.
- File rich bug reports with relevant context, stack traces, and more on Jira in a single click.
- Access every log – framework, video, screenshot, terminal, network & even application logs – chronologically sorted in a single pane. Dig into past logs to debug at the source.
- Troubleshoot test suite health with built-in dashboards for metrics like stability and flakiness. Set email alerts to get daily summaries & build insights.
Flaky Test Prevention and Best Practices
Following best practices is essential to lessen the chances of flaky tests. Some of the recommended best practices are:
- Test Isolation: It reduces dependencies and lessens the chances of interfering between tests, thus reducing the possibility of flakiness.
- Test Data Management: Institute proper test data management practices to retain reliability and consistency. Avoid using mutable or shared test data that can lead to flakiness.
- Optimal Test Timing: Schedule your tests to run perfectly for your team and testing environment. Consider factors such as network congestion, system load, etc., influencing test reliability.
- Synchronization Mode: Use suitable synchronization techniques in the test code to confirm appropriate synchronization between the application & test code. Utilize explicit waits, wait conditions, or synchronization methods provided by your automated test framework.
- Fine-Tune Operation Order: Fine-tune the sequence of operations within your tests to decrease concurrency and diminish dependencies. By carefully ordering test actions, you can control the odds of conditions or conflicts that can cause flakiness.
- Stable Test Environment: Manage a consistent and stable test environment. This includes controlling external factors (like system resources or network connectivity), managing dependencies, and confirming the accessibility of essential resources for test implementation.
- Continuous Monitoring and Feedback: Execute continuous monitoring of test outputs and gather feedback from the QA team. Encourage testers to report & address any potential flakiness they encounter. Regularly review and take proactive measures to resolve them.
To Sum Up,
By executing several techniques and leveraging robust tools like BrowserStack Test Observability and TurboScale, QA and software development teams can overcome the hurdles imposed by flaky tests and accomplish an effective and smooth development experience. Incorporating these tools improves confidence and empowers teams to tackle flaky tests head-on, ensuring an accurate test workflow.
1. Why are flaky tests problematic in software testing?
These tests can be problematic in QA testing for myriad reasons. They can cause unreliable test outcomes, making it easier to define the actual quality of the software being tested. Flaky tests can also waste effort and time as they necessitate extra analysis and retesting.
2. What are the common causes of flaky tests?
Flaky tests can be caused by multiple factors, counting timing issues, environmental issues, race conditions, synchronization issues, external dependencies, test environment inconsistency, improper test design, and non-deterministic application behavior.
3. How can flaky tests be identified & resolved?
It is crucial to analyze failure patterns, test logs, and implementation history to detect flaky tests. Monitoring tools and devoted flaky test detection frameworks can also assist in detecting flakiness. Once flaky tests are detected, they can be resolved by synchronization methods, stabilizing the test environment, & implementing best practices.
4. How can the influence of flaky tests be diminished?
The impact of these tests can be reduced by establishing proactive actions, implementing effective strategies to control flakiness, and following best practices.
5. Can flaky tests be eliminated completely?
Eliminating flaky tests can be tricky and challenging, but their impact can be significantly reduced with best practices and proactive measures.