Key Elements to Look for in Code Reviews of Unit Tests

Note: This article is based on insights from my experience as an SEOer, working at Typemock, a leading unit test company.

Introduction

When conducting code reviews of unit tests, it’s crucial to ensure that the tests are effective, reliable, and maintain the integrity of your codebase. This article will highlight key elements to consider during a code review of unit tests, providing best practices and tips to enhance the quality of your unit testing process.

Principles of Effective Unit Testing

How to Review Unit Tests Effectively

Ensure each test focuses on a single concept Adopt consistent and meaningful naming conventions Ensure tests are repeatable and do not rely on external factors Preferably, use mocking to isolate dependencies Prevent tests from containing logic or dynamic values Separate unit tests from integration tests Focus on testing public methods, as private or protected methods should rarely be in scope

Core Principles for Unit Test Review

Test Behavior, Not Implementation

When reviewing a unit test, it’s critical to ensure that the test does not focus on implementation details. Instead, focus on testing the public behavior defined by the interface. For example, if a function generates a random number, testing the specific sequence it generates is not ideal. Instead, ensure the test verifies the distribution properties.

Does the Test Actually Test Anything?

A common pitfall is when tests use generated ground truths based on their own code. This approach can lead to false negatives if a bug is introduced. Hard-code ground truths, unless absolutely necessary, and ensure that the ground truth is static and reliable.

Flakiness and Probability

Unit tests that involve randomness can be particularly flaky. Aim for a test failure rate (false negatives) of at most 10-10. While achieving this high level of accuracy can slow down tests, it’s essential for reliable test suites.

Coverage and Perfection

Evaluate whether the test covers all edge cases, common cases, and major code paths. Optimally, each unit test should cover some part of the code, and the tests should be fast enough to allow multiple runs. At Google, for example, code changes cannot be submitted if any affected tests fail. Ensure that each test runs efficiently and does not consume too much time.

Mutation Testing

Mutational testing is an advanced technique for evaluating the effectiveness of your tests. By subtly changing the code and observing if the tests fail, you can identify gaps in your test coverage. This method helps ensure that you have comprehensive and robust unit tests.

Conclusion

Effective unit testing is fundamental to building maintainable and reliable software. By adhering to these principles and best practices, developers can significantly enhance the quality of their unit tests, ensuring that they are robust, reliable, and provide accurate coverage of the codebase.