Just imagine. You’ve launched your brand new payment gateway for a flash sale, and suddenly transactions start failing. Customers are upset, and revenue is impacted. Eventually, you find out that there was a small bug in one function that should have been caught weeks earlier.
This nightmare scenario happens more often than you might think. Fortunately, unit testing in software testing can help you prevent these disasters. When a developer unit tests every module of code while it’s being built, bugs are caught when they’re cheap to find and fix.
Unit testing isn’t just about identifying bugs, however. It actually increases code quality, speeds up development, and creates confidence in your software. Let’s look at how unit testing works and why it is so important to the software project.
What is Unit Testing in Software Testing?
Unit testing is a software testing technique which allows developers to test small, individual parts, or units, of an application by themselves.
A unit might be a function, a method, or an object in object-orientated code.
The purpose of unit testing is to ensure that each unit functions as planned before developing larger units around it.
In the software development world, when someone asks what unit testing is, they are referring to testing code in the smallest sense. This has the added benefit of reducing dependencies, which usually makes testing faster and more reliable.
Unit testing is the first step in the puzzle of developing a highly stable application.
Example of Unit Testing
Imagine an online banking application that includes a function for calculating monthly interest. A unit test invokes this function using differing account balances, ensuring the interest calculation will always be accurate.
The test makes a number of statements about different scenarios. The test checks balances that are positive, zero, and also edge cases. If the interest rates dictate a new calculation, the unit test would detect any error in the calculated interest rate before end users ever saw it.
This relatively straightforward example illustrates the benefits of unit testing. One small function may get a very thorough verification. Any problems can be found during the development process rather than after it is in production.
5 Key Benefits of Unit Testing
The following are the 5 benefits of unit testing:
- Detecting Bugs Early
It’s much less expensive to uncover bugs during development than after deploying to production. Unit tests identify bugs immediately, as soon as you write the code. This helps prevent bugs from spreading throughout your codebase.
- Increasing Code Quality
Unit testing is intended to make sure each unit of code is working properly and that you are fulfilling the requirements, improving the quality of the application. It improves quality of the codebase since it encourages developers to think about how to test while writing code, resulting in better design quality.
- Provides Quicker Development Cycles
Automated unit tests can be run at nearly light speed. Typically, the developer gets immediate feedback regarding any changes. This helps to fast-track the development process, compared to manual testing.
- Improve Documentation
Tests are a form of living documentation. They communicate exactly how the functions should act. New developers can read a series of tests to understand code rather than Old documentation that may or may not be out of date.
- Reduces Debugging Time
When you are creating unit tests, you are going to spend less time trying to figure out what the bug was. The tests will tell you exactly which component is failing. You will be able to re-diagnose the bug much faster, which makes debugging far less stressful.
What is the Purpose of Unit Testing in Software Development?
The function of unit testing in software development encompasses more than just detecting bugs. It offers a safety net around your codebase. When you change code, the tests will let you know if something is broken.
Unit testing catches defects early, elevates the quality of the code, and has good compatibility with larger testing frameworks. Detecting bugs right away allows small issues to be identified before they cause system failure. This saves many hours of debugging and a lot fewer system crashes.
The Three Steps to the Unit Testing Process
Step 1: Arrange
The arrangement step creates all of the necessary items for the test. During this step, you may create test data, instantiate objects, and set up the environment. All of this prepares you to start testing with a clean slate.
Step 2: Act
The act step is where you are going to run the code being tested. In this step, you invoke your function or method with the test inputs. This is where the real action happens.
Step 3: Assert
The assert phase is where you verify results. In this step, you assert that the actual results of your function, method, or unit equal the expected results. If they do, your test passes. If they do not, your test fails, and you have discovered a bug.
Types of Unit Testing
- Manual Unit Testing (Manual Testing)
Manual unit testing is when the developers manually run tests. The developer simply provides some input and checks the output, which is fine for simple components or exploratory testing.
Manual unit testing requires much more time and effort than automated testing and contains opportunity for human error. However, it can also be beneficial in instances when automation is not an option or across smaller projects.
- Automated Unit Testing (Automated Testing)
Typically, the automation option is preferred, as it ensures unit tests are run most effectively, efficiently, and at scale. Automated programming uses the framework to automatically run a suite of tests. This is the standard in modern development.
Automated tests run very quickly and reliably; they do not make human errors. You can run your tests hundreds of times a day without additional effort, making it perfectly suitable for a continuous integration pipeline.
3 Unit Testing Strategies
- Test-Driven Development (TDD)
Test-Driven Development turns the original approach on its head. You create tests before the implementation of the actual code. Your tests validate that the code satisfies the original requirements from the outset.
Test-driven development TDD is a methodology that uses test cases to determine what the actual code should produce based upon the expected functionality, to ensure that the code satisfies the original requirements.
Test-driven development results in cleaner, better-organized code. Most importantly, test-driven development automatically builds the test suite for you.
- Behavior-Driven Development (BDD)
Behavior-Driven Development tests by behaviour as opposed to functional values were produced. Tests are written in natural language, making them more accessible to non-technical team members.
Behavior-driven development also bridges the gap between developers and business people. Everyone understands what is actually being tested. This helps build up communications between stakeholders and provides clarity around design and implementation.
- Mocking and Stubbing
Mocking and stubbing replace dependencies inside the application with controlled versions. Mocking and stubbing are able to isolate the unit being tested so one can test code without worrying about going to a database, REST API, or some other external system.
Mocks contrast interactions with dependencies, whereas stubs provide the reusable response data that one can program to every time the dependent is called. Mocking and stubbing help ensure that your tests only evaluate the unit under test.
Best 7 Practices for Unit Testing
- Write Tests During Development
It is recommended to write unit tests while you develop software, rather than afterward. This helps you identify bugs when they are fresh, as well as determine if your code is testable or not, and in the long run allows you to optimize your testing approach.
- Do Not Use Logic in Tests
Keep your unit tests as simplistic as possible. This means they should not have logical conditions. Unit tests must only verify expected behaviour and not the implementation. If you must include some logic, break your tests into simpler, smaller tests.
- Tests Must Not Depend on Each Other
Tests should run independently or not depend on a specific running order. You do not want tests depending on one another, in case they run in a different order. You also do not want tests that cause issues debug-wise in the future.
- Use Meaningful Test Names
Your test names should accurately describe the behaviour that is being verified. They will serve as documentation for your code. Descriptive test names will help other developers understand what each test is verifying almost immediately.
- Test as Much Coverage as Possible
You want to test as much code as possible. You should aim for a coverage percentage that is generally considered acceptable (70 to 80% +), noting that better coverage equates to a higher probability of catching bugs within the application; just don’t measure your tests by the number.
- Use Mocks and Stubs Wisely
Mocks and stubs are a great way to separate out a unit from its dependencies. This provides tests that run fast and reliably. However, don’t go overboard with mocks and stubs; during testing, some integration is needed for real-life testing.
- Run Tests in CI/CD Pipelines
Unit tests should be integrated into your CI pipeline. That is, tests should be automatically run on every commit. This helps catch any issue immediately, before it can be codified into other parts of the code.
Unit Testing vs Other Testing Types
Unit Testing vs Integration Testing
Unit testing focuses on verifying isolated components of code. Integration testing focuses on the interaction between two or more of the code’s units and whether they function correctly. Unit tests are usually faster and more focused than integration tests. Integration tests discover any errors in the interaction between components.
Unit Testing vs Regression Testing
Unit testing verifies a specific unit performs its intended functions. Regression testing makes sure new code or alterations to existing code do not break the software’s existing functionality. These have different purposes and both are important elements of a testing strategy.
3 Unit Testing Techniques
Here are the 3 unit testing strategies:
- Structural Testing (White Box Testing)
Structured testing evaluates your code structure. It is testing that a developer with knowledge of implementation will undertake. This verifies how the system carries out the task internally.
This testing requires a thorough knowledge of the code structure. It evaluates code paths, decision points, and loops, with the goal being to execute all paths of a given code.
- Functional Testing
Functional testing checks features have the desired functionality. You provide a value and make sure the value produced is what you expect. This method looks at what the code is doing and not how the code is doing it.
Functional tests validate systems against business requirements. It ensures the code does what it says it will do. This gives you confidence that the features you have executed will work respectively.
- Error-Based Testing
Error-based testing purposely inserts and creates errors into the code to ensure that the tests do in fact catch failures. Examples of this method of testing include mutation testing and fault seeding. The purpose of error-based testing is to simply verify that your tests are actually testing the code to ensure it is functioning.
Using historical test data can help determine which tests are most important to the process. This allows you to focus on the areas with the most experience and most impact on the testing process.
Top 8 Unit Testing Tools
Here are the top 8 unit testing tools:
- JUnit
JUnit is a widely used framework for unit tests in Java applications. It utilizes annotations (such as @Test, @Before, @After, @BeforeClass, @AfterClass) that essentially wrap test logic and help organize setup and teardown concerns. It also has seamless integration with Java IDEs.
JUnit is very lightweight and the most widely used framework. The framework, when set correctly, provides excellent support for employing test-driven development. It has a minimal number of assertions and a limited organization for tests. When engaging in advanced mocking, JUnit requires additional libraries like Mockito.
- NUnit
NUnit is a versatile and well-organized framework that handles any .NET language, including all versions of the .NET framework. NUnit has parallelization support for improved performance. Tests can run in parallel, which significantly decreases the time of a test suite.
NUnit includes support for multiple assertions and test runners. NUnit works with all versions of .NET runtime and across various platforms .NET is supported. The framework provides some advantages when testing complex situations. However, for a beginner, the learning curve is more advanced.
- Mocha
Mocha is an advanced JavaScript testing framework for Node.js applications. Mocha has excellent support for asynchronous testing. Mocha supports multiple reporters and custom output options.
Mocha is highly flexible and recommended when testing in the Node.js environment. As Mocha is JavaScript-based, it is a pretty seamless integration with the other JavaScript testing libraries, regardless of which options are preferred.
- Jest
Jest is a widely used JavaScript testing framework, especially for React applications. It has advanced code coverage analysis features that help ensure that all code paths are tested thoroughly. Jest comes with snapshot testing and built-in mocking capabilities.
Jest is quick and easy to get set up. It runs tests in parallel, which improves performance. Jest is intended for use with all front-end JavaScript frameworks and works well, though it may cause performance degradation when working with larger test suites.
xUnit.net is a modern testing framework designed for .NET. It can run tests in parallel, resulting in faster output. xUnit.net can be extended with custom libraries.
xUnit.net is optimized for .NET development. It also provides theory testing for multiple inputs. However, NUnit is still more commonly used, resulting in less community support around xUnit.net.
- TestNG
TestNG is a powerful and advanced Java testing framework. TestNG supports parallel execution and supports the use of a number of annotations. It allows data-driven testing, testing with multiple sets of data, and parameterized tests.
TestNG can integrate with a wide range of tools, such as Jenkins pipelines and CI/CD pipelines. TestNG can be advantageous for testing larger-scale applications.
- RSpec
RSpec is a behaviour-driven development (BDD) framework for the Ruby programming language. It allows for BDD writing-style testing to provide clarity and readability to tests while enabling the use of expressive syntax.
RSpec is designed specifically for Ruby developers. That’s a strength, as it’ll perform well in behaviour-driven testing, but it’s likely going to be slower than other simpler Ruby frameworks.
- Pytest
Pytest provides a simple way for developers to write and run unit test cases using the regular Python language assert statements. It relies on the concept of a fixture for controlling and managing the testing environment. It is also highly extensible due to the number of supported plugins.
Pytest is very scalable and flexible, and it has a readable syntax and structure to author tests simply.
5 Major Challenges in Unit Testing
The following are the five major challenges in unit testing:
- Dependency Management
Testing units with dependencies on external systems is challenging. Testing in isolation is complicated due to the need to mock these complex systems. Mocking is a time and skill-intensive process that is all too easy to get wrong.
- Mocking Complexity
Mocking is time-consuming, and accurate mocks have to behave just like the real systems they are mocking. If they do not, you are going to have a false sense of security and, as a result, miss additional bugs in testing.
- Flaky Tests
Tests can be flaky, meaning they work sometimes but not others. Flakiness arises from differences in the environment that can cause intermittent test failures. Oftentimes, tests are not designed very well and, in turn, are unreliable, thus making the developer frustrated when they are running tests.
- Time Invested
Writing a good set of unit tests takes a good amount of time. When it comes to legacy code, testing is even harder to do. Teams must find the right balance between time spent on testing and time spent on creating features.
- Test Maintenance
As code changes (which it will), tests will need to be updated or removed if they are no longer relevant, as old tests become unwieldy to maintain over time, a big burden given larger projects, and especially if they are complicated.
How to Measure Unit Testing Success?
- Code Coverage
Track the percentage of code that has tests written against it. You should strive for a minimum of 70-80% code coverage. Code coverage should just be used in conjunction with quality measures. Code coverage alone does not guarantee good software quality. Although code coverage is important, you want to focus on meaningful tests, not simply numbers.
- Pass Rate
Track how many tests pass versus fail. Healthy codebases contain tests that are passing consistently. A failing test run frequently indicates you may have a quality problem.
- Speed of Tests
Fast tests promote a culture of frequent testing, while slow test suites will discourage developers. Also, you will want to track execution time and optimize test performance regularly.
- Bug Detection
Track how many bugs are found by tests. The more effective your tests are, the more bugs you will find before production. For example, if your test suite identifies 96 bugs out of 100, this shows the value of utilizing tests.
- Developer Adoption
You want to track how often your teams, whether individual contributors or full teams are writing tests. High developer adoption is a measure you want to see that indicates a good quality of testing culture. Low developer adoption could indicate process problems or tool problems.
FAQs
What is a unit test in software testing?
A unit test is a script that tests a specific piece of code (a function or method), providing input and verifying the expected output.
Who does unit testing?
Developers typically write and run unit tests because they understand the code and logic.
What are the steps of unit testing?
Write the test, run the test, fix the code, and rerun the test until it passes.
What are the types of unit testing?
Manual unit testing and automated unit testing.
What is the purpose of unit testing in software development?
Unit testing is important to reduce the presence of bugs, improve code quality, speed up delivery, and maintain a stable code base as changes or enhancements are delivered.
Conclusion
In conclusion, unit testing is a foundation of software testing and is integral in providing reliable software. It identifies bugs at the earliest stage, it improves code quality, and it provides confidence when developing software.
Regardless of the type of software you are developing, unit testing will add meaningful value. Apart from lowering the number and severity of bugs, unit testing allows developing software faster and of better quality. Just start small, develop a habit of writing tests and see your code quality improve.
