Unit testing is a software development practice that involves testing individual units of code to ensure their correctness and functionality. These units are typically small, isolated portions of code, such as methods or functions.

The main purpose of unit testing is to verify that each unit of code works as expected in isolation before integrating them into larger modules or systems. Let’s break down these information and here are some important features of unit tests.

The FIRST principle is a set of guidelines or best practices for writing effective unit tests. It stands for:

  1. Fast: Tests should be fast and run quickly, allowing developers to get feedback on the code’s correctness as soon as possible.

  2. Isolated/Independent: Each test case should be independent of others, meaning that running one test should not affect the outcome of another test.

  3. Repeatable: Tests should be repeatable in any environment and produce consistent results each time they are executed.

  4. Self-validating: The result of a test should be either “pass” or “fail” without any manual interpretation required. Tests should check their own results automatically without relying on external validation.

  5. Timely: Unit tests should be written at the same time as the code they are testing or shortly after. Delaying test writing can lead to decreased effectiveness and potential bugs.

By following these principles, developers can ensure that their unit tests are reliable, maintainable, and provide accurate feedback on the quality of their code. Along with this principle, below are some important features of unit tests that should be kept in mind.

  • Small tests: Unit tests should be small. Usually the code base should be divided into smaller chunks of code as classes and methods. That will lead to smaller unit tests which tests specific functionalities. This is because by failure of the unit test, it should be easier to identify actual bug. If unit tests cover large code base in single test, we will need to read through that large code to understand the problem.
  • Automated: Unit tests can be deployed as part of CI/CD process. This allows us to repeat the tests everytime we push the code or at a scheduled time (may be everyday) to identify when our code is broken and easily fix bugs.
  • Use Descriptive Names: Test method names should always be descriptive and readable. There may be a convention your organization might be using but regardless test method names should be readable. For example, if we have a class under test, the test method should be something like testSomeFunction(). Another convention is to use very long descriptive names testMethodName_whenSomething_thenResult(). The names are important because in the test report, we can easily identify which test cases have failed based on these names. We can 100% change the names in the report if we wish using JUnit annotations.
  • Use Annotations: JUnit provides annotations @BeforeEach and @AfterEach to set up and tear down test data or any resources. We will see them in detail in another tutorial.

Why should we use Unit Tests?

There are several benefits to implementing unit tests in your projects:

  1. Early Bug Detection: Unit tests can identify bugs and issues early in the development process, allowing for efficient debugging and reducing the cost of fixing problems later on.

  2. Improved Code Quality: By writing tests, you are forced to think about how your code should behave and what edge cases should be handled properly. This leads to cleaner, more robust code.

  3. Ease of Refactoring: Having comprehensive unit tests gives you confidence when refactoring or making changes to your codebase. Tests act as a safety net, ensuring that existing functionality remains intact after modifications.

  4. Documentation: Tests serve as living documentation of how your code works and what it is expected to do. They provide insights into usage scenarios and can help other developers understand your codebase faster.

Setting up JUnit for Unit Testing

To set up JUnit in your existing projects, we only need to add JUnit dependency. This tutorial focuses on Maven but most dependency management software provides option to import external libraries.

Add JUnit Dependency

1<dependency>
2    <groupId>org.junit.jupiter</groupId>
3    <artifactId>junit-jupiter-api</artifactId>
4    <version>5.x.x</version>
5    <scope>test</scope>
6</dependency>

Once this dependency is added and imported, we can start writing Test classes and methods.