Unit testing is a vital practice for ensuring the quality and functionality of your code, especially in a continuous integration (CI) pipeline, where you need to deploy changes frequently and reliably. In this article, you will learn how to write effective unit tests for applications in a CI pipeline, covering the following aspects:
Unit tests are small, isolated, and automated tests that check the behavior and output of a single unit of code, such as a function, a class, or a module. They help you verify that your code works as expected, catch bugs early, and refactor with confidence. Unit tests are usually written in the same language as the code under test, using a testing framework or library that provides tools and conventions for writing and running tests.
CI is a process that involves integrating code changes from multiple developers into a shared repository and running automated tests and checks to ensure that the code is stable and ready for deployment. CI helps you deliver software faster, with fewer errors and conflicts, and with more feedback and visibility. Unit tests are essential for CI because they provide the first line of defense against bugs and regressions. They also enable you to test your code in isolation, without relying on external dependencies or environments, which makes them faster and more reliable than other types of tests.
There is no CI without unit tests: without unit tests, all you have is a remote compiler. Unit tests (as well as other forms of test automation) are the very essence of the idea of Continuous Integration, which is built on the principle that you can automatically verify the validity of a new release, and that no regressions have slipped into the build.
To write effective unit tests for applications in a CI pipeline, you should adhere to some best practices and principles. This includes writing clear, concise, and consistent test names and descriptions that explain what the test does and what it expects. The AAA pattern (Arrange, Act, Assert) is useful for structuring tests and separating the setup, execution, and verification phases. Furthermore, you should test one thing at a time and avoid testing multiple scenarios or behaviors in one test. Additionally, use test doubles (mocks, stubs, spies, etc.) to simulate and control the interactions and responses of external dependencies. Test data generators or factories can be used to create realistic and varied data for your tests; hard-coding or sharing data between tests should be avoided. Writing test cases for both happy and unhappy paths is also important, covering the expected and unexpected inputs, outputs, and edge cases. When using assertions and matchers, make sure they are specific, expressive, and meaningful; too many or too vague assertions in one test should be avoided. Lastly, code coverage tools can measure how much of your code is tested by your unit tests; aim for a high but realistic coverage percentage.
To write unit tests for a CI environment, your unit tests should be: - Fast (so they don't slow down your build process and give quick feedback) - Independent (so they don't rely on execution in a specific order, and can be run in parallel if you need to ) - Not rely on external systems or resources (so they aren't flaky) - Meaningful (so that you know why they break and what to do when they break) - Reproducible (they should produce the same result each time, or at least (for example for property testing) document the test cases well enough to identify a failing test case precisely) In other words (and I can't emphasise this enough), you should follow exactly the same principles that apply for normal unit testing.
In order to run your unit tests in a CI pipeline, you need to configure your CI tool or service to execute your tests automatically when code changes are pushed to the repository, or according to a predetermined schedule. Additionally, you should specify how to handle the test results, such as reporting the test status, duration, and output in a readable and accessible format (e.g., HTML, XML, or JSON), generating and displaying code coverage reports and metrics (e.g., line, branch, or function coverage), sending notifications or alerts to developers or stakeholders when tests fail or pass, or when coverage changes, and triggering or blocking the next steps in the pipeline (e.g., code analysis, integration testing, or deployment) based on the test outcome.
To ensure that your unit tests remain effective and relevant in a CI pipeline, you should adopt some practices and habits to maintain and improve your tests over time. This includes reviewing and refactoring tests with the same quality standards as production code, updating and adding tests whenever you change or add features, deleting or rewriting obsolete or redundant tests, using code analysis and testing tools to identify and fix code smells, bugs, or vulnerabilities, and seeking feedback from peers, customers, or users on how to improve your tests and testing process. Unit testing is a key skill for system development in a CI pipeline; by following these tips and guidelines, you can write effective unit tests that will help you deliver high-quality software faster with more confidence.