Gain insights into unit testing with JUnit 5. Learn about assertions, assumptions, nested and parameterized tests, advanced JUnit 5 concepts, and integrating tests with Maven and Gradle.

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junit5.tar.gz

mvn clean test

Unit Testing is a basic and essential skill to learn for any developer. In this course, you will learn what unit tests are, why they are important, and how to test your Java applications using the JUnit 5 Framework —  the most popular unit testing framework in the market for Java developers.

You will start with the fundamentals of Unit Testing and JUnit 5 and then gradually you will dive deep into the core concepts like assertions, assumptions, different types of tests like nested tests, parameterized tests, repeated tests, and more.

You will also learn some advanced concepts of JUnit 5 like the JUnit 5 extension model, dependency injection, how to migrate existing unit tests from JUnit 4 to JUnit 5, and how to integrate your unit tests with Maven and Gradle.

Unit Testing Java Applications using JUnit 5

Extensions can be registered in the following three ways.

- **Declarative Registration**: With the `@ExtendWith` annotation.
- **Programmatic Registration**: With the `@RegisterExtension` annotation.
- **Automatic Registration**: With the service loader mechanism.





# Declarative registration

For declarative registration, we use the `@ExtendWith` annotation on a test method or a class.

We use the following syntax to register an extension.


`@ExtendWith(MyExtension.class)`

There are two ways to register multiple extensions: we can pass multiple class references to the single annotations, or we define multiple `@ExtendedWith()` annotations. Both are shown below.

* **Passing multiple class references:** 
  ```
  @ExtendWith({MyExtension1.class, MyExtension2.class, MyExtension3.class})
  ```

* **Define multiple `@ExtendedWith()` annotations:**
  ```
  @ExtendWith(MyExtension1.class)
  @ExtendWith(MyExtension2.class)
  @ExtendWith(MyExtension3.class)
  ```

# Programmatic registration

We can also register the extension programmatically with the `@RegisterExtension` annotation in the test classes.

This annotation can also be used for static fields or instance fields.

# Automatic registration

Finally, we can automatically register our extensions with the service loader mechanism from `java.util.ServiceLoader`.

To register an extension, we need to create a file with the name `META-INF/services/org.junit.jupiter.api.extension.Extension` under the path `META-INF/services` in our JAR file.

We can add the details about the extension below inside the file.

`io.educative.junit5.extensions.SayHiExtension`

Then, we set the `junit.jupiter.extensions.autodetection.enabled` parameter to `true`. This enables automatic detection, which is disabled by default.


This configuration parameter can be supplied as a JVM system property, as shown below.

`-Djunit.jupiter.extensions.autodetection.enabled=true`

Understand different ways to register extensions in JUnit Jupiter.

Before We Begin

Introduction to JUnit 5

Junit 5 Core Concepts

Dynamic Tests

Dependency Injection in JUnit 5

JUnit 5 Extensions

Migrating from Junit 4 to Junit 5

Appendix

BONUS: Useful Assertion Libraries

Conclusion

Different Ways to Register Extensions

Declarative registration