In this blog, we’ll walk through the best practices for unit testing that every developer—whether beginner or seasoned—should follow to make their tests more effective, maintainable, and meaningful.
What is Unit Testing?
Unit testing involves testing individual units or components of a software application in isolation. A “unit” typically refers to the smallest testable part of an application—like a function, method, or class.
The goal is to verify that each unit performs as expected. Unit tests are usually automated and form the foundation of Test-Driven Development (TDD) and Continuous Integration/Deployment (CI/CD) pipelines.
- Write Independent and Isolated Tests
Each unit test should run independently of others. It should:
- Not rely on external systems (e.g., databases, APIs)
- Not depend on other test outcomes
- Leave no side effects (e.g., file changes)
This ensures consistent, predictable test runs and faster execution.
Tip: Use mocking tools like jest.mock(), unittest.mock, or Sinon.js to simulate dependencies.
- Use Descriptive Test Names
A good test name clearly states what is being tested and under what condition. It should be readable even by someone unfamiliar with the codebase.
Instead of:
test('test1', () => { ... });
Write:
test('should return total price including tax when valid input is given', () => { ... });
Readable test names improve team collaboration and debugging.
- Follow the AAA Pattern: Arrange, Act, Assert
This simple structure improves readability and clarity:
// Arrange
const cart = new ShoppingCart();
cart.addItem({ name: 'Laptop', price: 1000 });
// Act
const total = cart.calculateTotal();
// Assert
expect(total).toBe(1000);
- Arrange: Set up objects and inputs
- Act: Execute the function or logic
- Assert: Verify the output
4. Test One Thing Per Test
Avoid testing multiple behaviors in a single test case. Each test should verify a single responsibility. This makes it easier to spot the cause when a test fails.
Bad:
test('should return correct price and apply discount', () => {
// multiple checks in one test
});
Good:
test('should return correct price', () => { ... });
test('should apply discount', () => { ... });
5. Keep Tests Fast
Unit tests should be lightweight and fast. Avoid:
- Hitting databases or networks
- Doing expensive computations
- Relying on real external services
Slow tests reduce developer productivity and are more likely to be skipped.
6. Use Meaningful Assertions
Assertions are the core of unit tests. Make sure you're not just checking that something runs, but that it behaves as expected.
Instead of:
expect(result).toBeTruthy();
Use:
expect(result).toEqual([1, 2, 3]);
This provides clarity and improves failure debugging.
7. Avoid Logic in Tests
Don’t introduce unnecessary conditionals or loops in your test code. The test should be as deterministic and simple as possible.
Bad:
if (result.length > 0) {
expect(result[0]).toBe('Hello');
}
Good:
expect(result).toEqual(['Hello']);
8. Mock External Dependencies
If your unit interacts with services like APIs, databases, or file systems, mock them. This keeps tests deterministic and fast.
For example, using Jest:
jest.mock('./api');
api.fetchData.mockResolvedValue({ name: 'John' });
Use mocking frameworks such as:
- Jest (JavaScript)
- Mockito (Java)
- unittest.mock (Python)
9. Test Edge Cases and Failures
Don’t just test the happy path. Think about:
- What happens if inputs are null, undefined, or invalid?
- How does the function behave on empty arrays or large inputs?
- What happens when a service fails?
Robust software handles unexpected scenarios gracefully.
10. Maintain Your Test Code
Just like production code, test code should be:
- Readable
- Refactored regularly
- Free from duplication
If your tests are hard to understand or maintain, they become a liability instead of an asset.
11. Measure Code Coverage—but Don't Chase 100%
Tools like Istanbul (JavaScript), JaCoCo (Java), or Coverage.py (Python) help track test coverage. Aim for meaningful coverage, not just numbers.
Testing every line isn’t as important as testing important behaviors and edge cases.
Conclusion
Unit testing isn't just a formality—it's a crucial tool for building reliable, maintainable software. By following these best practices, you ensure your tests provide real value and don't become burdensome as your codebase grows.
To recap, remember to:
- Keep tests isolated and simple
- Name them clearly
- Test one thing at a time
- Handle edge cases
- Use mocks wisely
- Focus on meaningful assertions
In the long run, writing good unit tests saves time, reduces bugs, and improves developer confidence. Start small, stay consistent, and evolve your testing strategy as your project matures.
Read more on - https://keploy.io/blog/community/10-unit-testing-best-practices