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Effective unit testing

Flaky Tests

Sep 28, 2023

Unit testing stands as a cornerstone in contemporary software development, significantly elevating the overall quality and reliability of a software application. When practiced proficiently, unit testing through the paradigm of Test-Driven Development (TDD) ensures that testable individual units of code function in isolation as expected. This approach simplifies bug identification and resolution, supports refactoring efforts, and cultivates a robust and sustainable development process and codebase. To excel in creating high-quality unit tests, adhering to a set of best practices and principles is vital to the stability of your tests and product. Beat back flaky tests before they have an opportunity.

1. Isolate and Test One Thing at a Time

Adhering to the principle of testing one piece of code at a time promotes simplicity, focus, and ease of comprehension within each of your test cases. By isolating the unit being tested from the broader system, developers can swiftly pinpoint the cause of any failures and maintain a clean and manageable test suite. Over time, you can build up to integration testing where you test the product as a whole.

2. Craft Descriptive and Clear Test Names

Employing clear and descriptive test names that encapsulate purpose and expected outcomes improves the readability and documentation aspects of the codebase. Ensuring that developers can comprehend the test intent and context merely by reading the name enhances code clarity and minimizes ambiguity.

3. Follow the AAA Pattern: Arrange, Act, Assert

Adhering to the Arrange-Act-Assert pattern in test writing enhances readability and structure. This pattern involves arranging necessary preconditions and inputs, acting on the system, and asserting the expected behavior or outcome. This structured approach aids in quick issue identification and debugging.

4. Effectively Use Setup and Teardown When Necessary

Strategically utilize setup and teardown methods to create a consistent and controlled environment for tests. These aids in maintaining a clean test suite while ensuring tests remain independent and avoid unnecessary interdependencies.

5. Maintain Independence and Order Agnosticism of Tests

Write tests that can run independently and in any order. This practice ensures that a single test's outcome does not affect another, fostering a more reliable and predictable test suite. Avoid introducing dependencies or relying on specific execution orders.

6. Comprehensively Test All Code Paths

Strive for comprehensive test coverage, encompassing all possible code paths, including edge cases and error handling scenarios. This meticulous testing approach unveils potential issues that might remain concealed during normal execution.

7. Optimal Usage of Mocks and Stubs

Isolate the unit being tested from its dependencies by effectively employing mocks and stubs. Mocks simulate behavior, while stubs provide controlled responses, ensuring the test outcome is solely influenced by the unit under examination.

8. Regularly Refactor Tests

Refactor tests in a manner akin to production code, prioritizing cleanliness, maintainability, and the "Don't Repeat Yourself" (DRY) principle. Eliminate redundancy, enhance readability, and keep tests updated to align with evolving application requirements.

9. Leverage Automated Testing and Continuous Integration

Manual testing can create inconsistencies in your software testing practices. It is best to configure automated testing and integrate it into your continuous integration workflow. This practice ensures that tests are executed with every code change, enabling early issue detection and bolstering confidence in the codebase's stability.

10. Monitor and Analyze Test Results with Specialized Tools

Regularly monitor test results using specialized testing tools to identify patterns, detect areas that necessitate improvement, and track test performance over time. Analyze failures and adjust tests accordingly to optimize their efficacy and coverage.

11. Integrate Testing Tools for Enhanced Efficiency

Leverage dedicated testing tools like JUnit, which is widely used in Java development, or other unit testing frameworks specific to your programming language. Additionally, consider employing BuildPulse Code Coverage to monitor and enhance source code coverage, ensuring a well-tested, stable, and secure end product.

Conclusion

In conclusion, mastering the art of writing high-quality unit tests is paramount for every software developer. By diligently following these best practices and principles, developers can create efficient, maintainable, and reliable unit tests that significantly contribute to the overall success of their software projects. BuildPulse can help you identify problematic areas of your testing infrastructure that need investment - helping you get ahead of the problem. Remember, investing effort into creating robust unit tests pays off in terms of improved code quality, expedited development, and a resilient application in the long run.

FAQ

What is the difference between a flaky test and a false positive?

A false positive is a test failure in your test suite due to an actual error in the code being executed, or a mismatch in what the test expects from the code.

A flaky test is when you have conflicting test results for the same code. For example, while running tests if you see that a test fails and passes, but the code hasn’t changed, then it’s a flaky test. There’s many causes of flakiness.

What is an example of a flaky test?

An example can be seen in growing test suites - when pull request builds fail for changes you haven’t made. Put differently, when you see a test pass and fail without any code change. These failed tests are flaky tests.

What are common causes of flakiness?

Broken assumptions in test automation and development process can introduce flaky tests - for example, if test data is shared between different tests whether asynchronous, high concurrency, or sequential, the results of one test can affect another. 

Poorly written test code can also be a factor. Improper polling, race conditions, improper event dependency handling, shared test data, or timeout handling for network requests or page loads. Any of these can lead to flaky test failures and test flakiness.

End-to-end tests that rely on internal API uptime can cause test flakiness and test failures.

What's the impact of flaky tests?

Flaky tests can wreck havoc on the development process - from wasted developer time from test retries, to creating bugs and product instability and missed releases, time-consuming flaky tests can grind your development process to a halt.

What is the best way to resolve or fix flaky tests?

Devops, software engineering, and software development teams will often need to compare code changes, logs, and other context across test environments from before the test instability started, and after - adding retries or reruns can also help with debugging. Test detection and test execution tooling can help automate this process as well. 

BuildPulse enables you to find, assess impact metrics, quarantine, and fix flaky tests.

What are some strategies for preventing flaky tests?

Paying attention and prioritizing flaky tests as they come up can be a good way to prevent them from becoming an issue. This is where a testing culture is important - if a flaky test case is spotted by an engineer, it should be logged right away. This, however, takes a certain level of hygiene - BuildPulse can provide monitoring so flaky tests are caught right away.

What type of tests have flaky tests?

Flaky tests can be seen across the testing process - unit tests, integration tests, end-to-end tests, UI tests, acceptance tests.

What if I don't have that many flaky tests?

Flaky tests can be stealthy - often ignored by engineers and test runs are retried, they build up until they can’t be ignored anymore. These automated tests slow down developer productivity, impact functionality, and reduce confidence in test results and test suites. Better to get ahead while it’s easy and invest in test management.

It’s also important to prevent regressions to catch flakiness early while it’s manageable.

What languages and continuous integration providers does BuildPulse work with?

BuildPulse integrates with all continuous integration providers (including GitHub Actions, BitBucket Pipelines, and more), test frameworks, and workflows.

Combat non-determinism, drive test confidence, and provide the best experience you can to your developers!

How long does implementation/integration with BuildPulse take?

Implementation/integration takes 5 minutes!

What is the difference between a flaky test and a false positive?

A false positive is a test failure in your test suite due to an actual error in the code being executed, or a mismatch in what the test expects from the code.

A flaky test is when you have conflicting test results for the same code. For example, while running tests if you see that a test fails and passes, but the code hasn’t changed, then it’s a flaky test. There’s many causes of flakiness.

What is an example of a flaky test?

An example can be seen in growing test suites - when pull request builds fail for changes you haven’t made. Put differently, when you see a test pass and fail without any code change. These failed tests are flaky tests.

What are common causes of flakiness?

Broken assumptions in test automation and development process can introduce flaky tests - for example, if test data is shared between different tests whether asynchronous, high concurrency, or sequential, the results of one test can affect another. 

Poorly written test code can also be a factor. Improper polling, race conditions, improper event dependency handling, shared test data, or timeout handling for network requests or page loads. Any of these can lead to flaky test failures and test flakiness.

End-to-end tests that rely on internal API uptime can cause test flakiness and test failures.

What's the impact of flaky tests?

Flaky tests can wreck havoc on the development process - from wasted developer time from test retries, to creating bugs and product instability and missed releases, time-consuming flaky tests can grind your development process to a halt.

What is the best way to resolve or fix flaky tests?

Devops, software engineering, and software development teams will often need to compare code changes, logs, and other context across test environments from before the test instability started, and after - adding retries or reruns can also help with debugging. Test detection and test execution tooling can help automate this process as well. 

BuildPulse enables you to find, assess impact metrics, quarantine, and fix flaky tests.

What are some strategies for preventing flaky tests?

Paying attention and prioritizing flaky tests as they come up can be a good way to prevent them from becoming an issue. This is where a testing culture is important - if a flaky test case is spotted by an engineer, it should be logged right away. This, however, takes a certain level of hygiene - BuildPulse can provide monitoring so flaky tests are caught right away.

What type of tests have flaky tests?

Flaky tests can be seen across the testing process - unit tests, integration tests, end-to-end tests, UI tests, acceptance tests.

What if I don't have that many flaky tests?

Flaky tests can be stealthy - often ignored by engineers and test runs are retried, they build up until they can’t be ignored anymore. These automated tests slow down developer productivity, impact functionality, and reduce confidence in test results and test suites. Better to get ahead while it’s easy and invest in test management.

It’s also important to prevent regressions to catch flakiness early while it’s manageable.

What languages and continuous integration providers does BuildPulse work with?

BuildPulse integrates with all continuous integration providers (including GitHub Actions, BitBucket Pipelines, and more), test frameworks, and workflows.

Combat non-determinism, drive test confidence, and provide the best experience you can to your developers!

How long does implementation/integration with BuildPulse take?

Implementation/integration takes 5 minutes!

What is the difference between a flaky test and a false positive?

A false positive is a test failure in your test suite due to an actual error in the code being executed, or a mismatch in what the test expects from the code.

A flaky test is when you have conflicting test results for the same code. For example, while running tests if you see that a test fails and passes, but the code hasn’t changed, then it’s a flaky test. There’s many causes of flakiness.

What is an example of a flaky test?

An example can be seen in growing test suites - when pull request builds fail for changes you haven’t made. Put differently, when you see a test pass and fail without any code change. These failed tests are flaky tests.

What are common causes of flakiness?

Broken assumptions in test automation and development process can introduce flaky tests - for example, if test data is shared between different tests whether asynchronous, high concurrency, or sequential, the results of one test can affect another. 

Poorly written test code can also be a factor. Improper polling, race conditions, improper event dependency handling, shared test data, or timeout handling for network requests or page loads. Any of these can lead to flaky test failures and test flakiness.

End-to-end tests that rely on internal API uptime can cause test flakiness and test failures.

What's the impact of flaky tests?

Flaky tests can wreck havoc on the development process - from wasted developer time from test retries, to creating bugs and product instability and missed releases, time-consuming flaky tests can grind your development process to a halt.

What is the best way to resolve or fix flaky tests?

Devops, software engineering, and software development teams will often need to compare code changes, logs, and other context across test environments from before the test instability started, and after - adding retries or reruns can also help with debugging. Test detection and test execution tooling can help automate this process as well. 

BuildPulse enables you to find, assess impact metrics, quarantine, and fix flaky tests.

What are some strategies for preventing flaky tests?

Paying attention and prioritizing flaky tests as they come up can be a good way to prevent them from becoming an issue. This is where a testing culture is important - if a flaky test case is spotted by an engineer, it should be logged right away. This, however, takes a certain level of hygiene - BuildPulse can provide monitoring so flaky tests are caught right away.

What type of tests have flaky tests?

Flaky tests can be seen across the testing process - unit tests, integration tests, end-to-end tests, UI tests, acceptance tests.

What if I don't have that many flaky tests?

Flaky tests can be stealthy - often ignored by engineers and test runs are retried, they build up until they can’t be ignored anymore. These automated tests slow down developer productivity, impact functionality, and reduce confidence in test results and test suites. Better to get ahead while it’s easy and invest in test management.

It’s also important to prevent regressions to catch flakiness early while it’s manageable.

What languages and continuous integration providers does BuildPulse work with?

BuildPulse integrates with all continuous integration providers (including GitHub Actions, BitBucket Pipelines, and more), test frameworks, and workflows.

Combat non-determinism, drive test confidence, and provide the best experience you can to your developers!

How long does implementation/integration with BuildPulse take?

Implementation/integration takes 5 minutes!

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