Last updated on Aug 5, 2024

What are some common unit testing pitfalls or anti-patterns to avoid?

Unit testing is a vital part of code quality and reliability, but it can also be a source of frustration and confusion if done poorly. In this article, we will explore some common unit testing pitfalls or anti-patterns to avoid, and how to improve your tests with peer review and best practices.

1 Test too much or too little

One of the biggest challenges of unit testing is finding the right balance between testing too much or too little. Testing too much can lead to brittle, slow, and redundant tests that are hard to maintain and debug. Testing too little can leave gaps in your code coverage and expose you to bugs and errors that could have been prevented. A good rule of thumb is to test only the public interface and behavior of your unit, and not the internal implementation details. You should also avoid testing trivial or obvious code, such as getters and setters, unless they have some logic or side effects.

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2 Test the wrong thing

Another common pitfall of unit testing is testing the wrong thing, or testing something that is not a unit. A unit is the smallest testable piece of code that can be isolated from its dependencies and environment. For example, a unit could be a function, a class, or a module. Testing something that is not a unit, such as a database query, a web service call, or a user interface, can make your tests unreliable, slow, and dependent on external factors. These types of tests are better suited for integration or end-to-end testing, which verify how different units work together. To test a unit, you should use mocks, stubs, or fakes to simulate its dependencies and isolate it from the rest of the system.

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Yuvaraj Madheswaran

GM Financial
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Isolated Units vs. Integrated Components: A unit test should focus on the smallest testable component of an application, such as a function or a class. It's essential to isolate this unit from its dependencies to ensure the test accurately reflects the unit's behavior. Mocks, Stubs, and Fakes: To effectively isolate the unit, mocks (or stubs and fakes) are used to simulate dependencies like databases or web services. This ensures the unit test is only verifying the logic within the unit itself. Integration Testing for Interconnected Systems: Integration tests are better suited for scenarios where the interaction between multiple units or systems needs verification. They ensure that the components work together as expected.

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3 Test with bad data

A third common pitfall of unit testing is testing with bad data, or data that is unrealistic, incomplete, or inconsistent. Testing with bad data can lead to false positives, false negatives, or irrelevant results. For example, testing with empty strings, null values, or zero numbers can mask potential errors or edge cases in your code. Testing with data that is too similar, too random, or too hard-coded can also reduce the effectiveness and readability of your tests. To test with good data, you should use realistic and representative data that covers different scenarios and inputs. You should also use data generators or factories to create and manage your test data dynamically and avoid duplication.

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Yuvaraj Madheswaran

GM Financial
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Risk of False Positives/Negatives: Testing with unrealistic or incomplete data increases the likelihood of encountering false positives or false negatives. In financial services, false positives in fraud detection can lead to unnecessary customer inconvenience, while false negatives can result in undetected fraudulent activities. Edge Cases Consideration: Failure to consider edge cases can result in overlooking critical issues. In the context of financial services, this could mean neglecting to test scenarios such as negative loan amounts or extremely large transaction volumes.

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4 Write bad tests

A fourth common pitfall of unit testing is writing bad tests, which can be unclear, complex, or inconsistent. This can make tests hard to understand, modify, or reuse, as well as introduce bugs or errors in your code that can affect the quality and confidence. To write good tests, you should use descriptive and meaningful names for your tests, test cases, and test data. Additionally, use a consistent format such as the AAA pattern (Arrange, Act, Assert), a testing framework and tools that suit your needs (such as Jest, Mocha, or Jasmine), specific and accurate assertions (not too many or too few per test), and comments and documentation to explain the purpose of the test without repeating what the code already says.

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Yuvaraj Madheswaran

GM Financial
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Lack of Descriptive and Meaningful Names: Using generic or ambiguous names for tests, such as testFunction1 or testMethodA Inconsistent or Complex Test Structure: Tests that do not follow a consistent structure can be hard to read and maintain Overly Complex Tests: Writing tests that are too complex or test multiple aspects of the code simultaneously Inaccurate or Non-Specific Assertions: Using too many or too few assertions, or assertions that are not specific enough Lack of Comments and Documentation: Tests without comments or documentation can be difficult to understand, especially for new team members.

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5 Skip peer review

A fifth common pitfall of unit testing is not getting feedback and suggestions from other developers on your tests. This can lead to missed opportunities to improve your tests, fix errors, or learn new techniques. To ensure that your tests are consistent, readable, and maintainable across your team and project, you should utilize a code review tool or platform, such as GitHub, GitLab, or Bitbucket. Additionally, following a code review checklist or guideline, such as Google's code review guide, is essential for covering the essential aspects of your tests. It is important to be respectful, constructive, and open-minded when giving and receiving feedback while avoiding personal or subjective comments. Once feedback has been incorporated into your tests, thank the reviewers for their time and effort. Unit testing can be difficult but is worth it if you follow these best practices. You can write better tests that will improve your code quality and reliability while also learning from your peers and sharing knowledge with them. Happy testing!

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What are some common unit testing pitfalls or anti-patterns to avoid?

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1 Test too much or too little

2 Test the wrong thing

3 Test with bad data

4 Write bad tests

5 Skip peer review

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