What is Unit Testing?

Introduction

Jacob Kaplan-Moss, one of the leading developers and co-creators of the Django Python framework, said:

Code without tests is broken by design

In this article, we are going to discuss Unit Testing. Firstly, software testing, in general, is an important part of software engineering that involves evaluating an application to identify issues before it is released to users. This ensures that the application or software meets the specified requirements and performs as expected.

There are many types of software testing, common ones include unit testing, integration testing, system testing, and end-to-end (E2E) testing. Each type of software testing serves a specific purpose and is done at different stages of the software development lifecycle.

This article aims to give a comprehensive understanding of unit testing. By the end, you will have gained insights into what unit testing is, its benefits, how it is implemented, best practices, and scenarios where it might or might not be suitable. This knowledge will equip you with the necessary information to effectively incorporate unit testing into your software development process.

Understanding Unit Testing

Unit testing is a type of software testing where small blocks or units of a software application are tested to make sure they work perfectly on their own. A "unit" in unit testing can be looked at as a piece of a module, the smallest testable part, like a function or method. The main goal of unit testing is to ensure that each unit of the software behaves as expected independently.

Unit testing differs from other types of software testing in the following ways:

• Integration Testing: This type of software testing focuses on how different components of the software interact with each other. It ensures that the integrated units function as intended. On the other hand, Unit testing aims at ensuring each unit functions as expected independently.

• System Testing: System testing assesses the whole integrated software application, ensuring that it satisfies the criteria or meets the requirements of the application. It tests the system as a whole while unit testing deals with individual units.

• End-to-End (E2E) Testing: E2E testing assesses the complete application from start to end by simulating real-world user scenarios. It is normally performed by beta testers. It ensures that the application functions as expected in a practical setting. On the other hand, unit testing focuses on the function of individual units.

Analogy

Let’s use a real-world example to illustrate what unit testing could look like. Consider a car manufacturing company. Here, unit testing would be compared to examining individual parts of the car, such as the engine, brakes, or steering wheel, separately to make sure they work correctly before putting/assembling the car together. Integration testing would be testing how the components work together, while system testing would examine the entire car as a whole, and lastly, E2E testing would simulate driving the car on the road to determine its performance under real-world conditions.

Benefits of Unit Testing

Unit testing provides several benefits that enhance the software’s overall quality and maintainability. Below, let’s discuss some of these benefits.

• Early Bug Detection: By testing separate units early in the process of development, bugs and defects can be easily exposed and fixed before they affect other parts of the application. In return, the cost and effort placed into debugging are greatly reduced.

• Improved Code Quality: Carrying out unit tests allows the developers to write a much more maintainable and properly structured code. This helps in exposing the flaws in design and highlights the areas that need improvement.

• Faster Development: Writing unit tests usually seems time-consuming, but it can speed up the development of an application in the long run. Through catching bugs early, developers spend less time debugging and more time creating/writing new features. You can also save time by automating unit testing using Keploy.

• Regression Testing: Unit tests act as a safety net, especially when making changes to the codebase. Unit tests can quickly expose the unintended side effects or regressions that arise when new changes are introduced into the existing code during development.

• Documentation: Unit tests are a form of documentation that lays down clearly how each section of code is intended to be used. This is especially important when new developers or new members of the team have to be brought up to speed with the progress of the software.

• Confidence in Refactoring: Refactoring is the process of improving the structure of existing code without changing what it does or the external behavior. Unit tests provide confidence that the refactored code still works as expected, allowing developers to make changes more freely.

Unit Testing in Practice

In this section, let’s discuss some practical implementations of Unit Testing and the popular tools and frameworks used.

Common Tools and Frameworks

Many tools and frameworks are already out there and readily available to assist in unit testing in different programming languages. Here are popular ones in the Python community.

• unittest

  This is a built-in testing framework in Python that provides a rich set of tools for writing and running tests.

• pytest

  This is a third-party testing framework that is more flexible and easier to use than the built-in unittest framework. It supports fixtures, parameterized tests, and so much more.

Below is an example of a simple unit test using the unittest framework in Python.

python
import unittest 
def add(a, b):
    return a + b
class TestAddFunction(unittest.TestCase):
    def test_add_positive_numbers(self):
        self.assertEqual(add(2, 3), 5)

    def test_add_negative_numbers(self):
        self.assertEqual(add(-1, -1), -2)

    def test_add_positive_and_negative_numbers(self):
        self.assertEqual(add(-1, 2), 1)

if __name__ == '__main__':
    unittest.main()

In the above example, we defined a simple add function and wrote three test cases to verify the way it behaves with different inputs. For example, the test_add_positive_numbers() function tests if the dd(2,3), which is an addition of two positive numbers, returns an output of 5 as required.

For the JavaScript community, the popular unit testing tools include:

• Jest

  This is a popular testing framework for JavaScript and React applications. It provides an intuitive API for writing tests and has features like code coverage reporting.

• Mocha

  This is another JavaScript testing framework that is often used in combination with assertion libraries like Chai. It is flexible and extensible.

Here is an example of a simple unit test using the Jest framework in JavaScript.

javascript
// add.js
function add(a, b) {
    return a + b;
}

module.exports = add;

// add.test.js
const add = require('./add');

test('adds 2 + 3 to equal 5', () => {
    expect(add(2, 3)).toBe(5);
});

test('adds -1 + -1 to equal -2', () => {
    expect(add(-1, -1)).toBe(-2);
});

test('adds -1 + 2 to equal 1', () => {
    expect(add(-1, 2)).toBe(1);
});

In this example, we define a simple add function and write three test cases to verify its behavior with different inputs using Jest's testing API. It is an implementation of our tests in the earlier example, but in this case, using JavaScript.

Keploy is another tool that can be used for unit testing. With it, you can automate the generation of unit tests for multiple programming languages.

Best Practices in Unit Testing

Many new developers struggle with how to best implement unit tests. Let’s discuss some of the best practices to follow to get the most out of unit testing, as it is important to follow best practices. Here are some key recommendations:

• Test one thing at a time

  Each of the tests performed should focus on a single aspect or behavior of the unit being tested. This makes it easier to uncover the cause of failures, and it also ensures that tests are more maintainable.

• Use meaningful names

  Test names should clearly describe what is being done or tested. This makes it easy for developers to understand the purpose of each test.

• Keep tests independent

  Tests should not depend on other tests. Each test should be able to run independently and in any order.

• Test both happy and sad paths

  Make sure that both the expected (happy) paths and the unexpected (sad) paths are tested. Happy path testing looks at how the product works under perfect conditions; unhappy path testing looks at what happens when things go wrong. Tests should include testing the edge cases and potential error scenarios as well. For example, someone adds more items to the cart than items in stock.

• Write tests before code (Test-Driven Development)

  Following a test-driven development (TDD) approach helps ensure that code is testable right from the beginning. Write tests before implementing the code to guide the development process.

• Run tests frequently

  It’s not enough to know about unit testing. Include unit tests in the development workflow and frequently run them, ideally as part of a continuous integration (CI) pipeline. This approach catches issues early and ensures that tests are always up-to-date.

• Automate your unit tests

  Automating your unit tests helps you catch bugs early before pushing to production. Keep in mind bugs in production are 100x more expensive to fix. Keploy provides a tool for automating unit tests.

When to Avoid Unit Testing

While unit testing is mostly beneficial, there are some scenarios where it might not be the best approach. Below is a discussion on this.

• Legacy code

  When working with legacy code that was developed without testability in mind, introducing and carrying out unit tests can be time-consuming and not the best approach. In these scenarios, one can focus on system testing instead.

• Prototyping

  In the initial stage of prototyping, the primary goal is to quickly iterate and explore many ideas, and unit testing can significantly slow down the development process in this case. So, in this scenario, unit tests are introduced when the application is now stable.

• Very small projects

  Simple projects that have minimal complexity in their development do not require unit testing; rather, higher-level tests can be carried out.

Conclusion

Unit testing is crucial in software engineering in that it offers numerous benefits. Performing unit tests allows developers to detect bugs early, improve code quality, develop systems faster, and even increase confidence in refactoring. By understanding what unit testing is, its benefits, and how to implement it effectively, developers can write more reliable and maintainable code. Tools like Keploy can further streamline testing by auto-generating test cases,, automating unit tests thus reducing manual effort and saving time. However, we highlighted different types of testing at the start of this article, so it is important to note that unit testing is not a one-size-fits-all solution and should be used based on the context and requirements of the project.

FAQs

1. Why is unit testing important?

Unit testing helps catch bugs in code early and ensures the correct functionality of code.

2. What is the difference between unit testing and integration testing?

Unit testing checks individual functions/components, while Integration testing checks how different modules function together.

3. How can Keploy help with unit testing?

Keploy helps with the auto-generation of unit test cases and test data that replicate real-world scenarios. It also brings you automated unit testing and continuous integration (CI) testing.

4. How does Keploy differ from other unit testing tools?

Keploy differs from other traditional unit testing tools in that it brings automation to unit testing, unlike other tools. It also supports multiple programming languages and tech stacks, unlike other tools.