Unit Testing Best Practices: 10 Ways To Make The Most Out Of Your Tests

When Google’s Web Server team introduced a unit testing culture, they determined that no code or code review should be accepted without accompanying unit tests. This made an incredible difference, and they were able to reap numerous benefits from the practice. It geared up their development speed, increased test coverage, and significantly reduced the number of defects, production rollbacks, and emergency releases.

Overall, unit testing disciplined the entire team and remained as concrete documentation for new members joining the team. No wonder unit testing is adopted by many organizations to prevent buggy code and enhance software quality.

However, organizations may fail to get the desired output from the unit testing process if not done right. This blog introduces you to some best ways to integrate unit testing in your development and testing cycle so that you can reap the most benefits of this essential testing strategy.

What is Unit Testing?

Unit testing is a type of testing in which one segregates the code into the smallest, testable units that can be logically isolated from the program. These units are then tested individually to check if each performs as expected. The small units make it easier to design tests, execute, record, and analyze results than larger chunks of code. It allows you to locate the errors quickly and fix them early in the development cycle. Unit tests are types of functional tests that are written and run by software developers.

Role of Unit Testing

• Provides early, rapid and continuous feedback in SDLC.
• Offers super-precise feedback with their laser-sharp focus.
• Ensures quality standards are met before deploying the product.
• Created by software engineers to verify how units work when completely isolated. Developers use test doubles like stubs, mock objects, etc., to replace the missing parts in a test module for isolated testing.
• It enables continuous testing in-app modules without any hassles of dealing with external services or dependencies.
• Overall, it provides developers with a reliable engineering environment where efficiency, productivity, and quality code are paramount.

Characteristics of A Good Unit Test

• Fast: Unit tests should run quickly since a project can have thousands of unit tests.
• Reliable: Reliable unit tests only fail if there is a bug in the underlying code, which is pretty obvious. But at times, tests fail even if there are no bugs in the source code due to a design flaw.
• Isolated: Unit tests are run in isolation without any interdependencies and external dependencies (file system, database, etc.) or external environment factors.
• Self-checking: Unit tests should automatically determine if they passed or failed without any human intervention.
• Timely: If a unit test code takes longer to write than the time taken for writing the code being tested, consider a more viable design.
• Truly unit, not integration: Unit tests can easily turn into integration tests if tested together with multiple other components. Unit tests are standalone and should not be influenced by external factors.

Unit Testing Best Practices

1. Write Readable Tests
Easy-to-read tests are comforting to understand how your code works, its intent, and what went wrong when the test fails. Tests revealing the setup logic at first glance are more convenient for figuring out how to fix the problem without debugging the code.

2. Avoid magic numbers and magic strings
The use of magic strings or numbers confuses readers since it makes the tests less readable. In addition, it diverts readers from looking at the implementation details and makes them wonder why a particular value has been chosen instead of focusing on the actual test.

3. Write Deterministic Tests
Deterministic tests either pass all the time or fail all the time until fixed. But they exhibit the same behavior every time they are run unless the code is changed. So a flaky test, aka a non-deterministic test that sometimes passes and sometimes fails, is as good as having no test at all.

4. Avoid test interdependencies
Test runners generally run multiple unit tests at a time without sticking to any particular order, so interdependencies between tests make them unstable and difficult to execute and debug. You should ensure each test case has its own setup and teardown mechanism to avoid test interdependencies.

5. Avoid logic in tests
Writing unit tests with logical conditions and manual strings concatenation increase the chances of bugs in your test suite. Tests should focus on the expected end result instead of the implementation details.

6. Refrain multiple asserts in a single unit test
For a unit test to be effective, keep one use case at a time, that is to have only one assertion in the tests. If you’re wondering what would happen if you include multiple assets in a single test, let’s take a simple example.

7. Keep your tests away from too many implementation details
Tests are difficult to maintain if they keep failing even for the slightest changes made to the implementation code. So the best bet is to keep implementation details at bay and save your time from rewriting the tests repeatedly. Thus, coupling tests with implementation details decrease the value of tests.

8. Write tests during development, not after it
Unit tests are at the base of the testing pyramid and are the earliest tests conducted in the development cycle. Therefore, they work best when they are run alongside the development and not after it.

9. Automate tests using CI/CD tools
Automating the tests by including them in a CI/CD pipeline allows you to easily run tests multiple times in a day. It enables continuous testing and test execution on each code commit. Even if you forget to run a test, the CI (Continuous Integration) server won’t and will prevent passing on buggy code to the customers.

10. Update the tests periodically
Unit tests are ideal for long-term projects since it helps new team members with detailed documentation by making the code and its behavior easier to understand. So maintaining and updating the tests periodically makes them ideal test suites for creating helpful documentation.

What about Code Coverage?

Code coverage measures how much of the code is actually executed by a test. It helps identify the untested parts of a codebase. So high code coverage is often used to indicate higher quality of code. Although it is not the sole measure of code quality, it is a useful tool. To state its importance, I would like to quote Adam Kolawa, co-founder and former CEO of Parasoft.

The Bottom Line

The above-mentioned best practices aren’t the only ways to maximize your outcomes, but they’d surely ease your unit testing process, with automation being the key. Also, what’s the best way to do unit testing than using its frameworks available in various languages to simplify the process? Except for some advanced features that need to be hand-coded for complex requirements. Unit testing, for one, is focused, unique and you cannot match its outcome with any other type of testing.

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