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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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

In previous `JUnit` versions, the constructors and methods in the tests did not have parameters. With `Jupiter`, it’s possible to define the constructor and method parameters. This enables `dependency injection` for our tests.

`Jupiter` provides the interface, `ParameterResolver`, which helps an API resolve the constructor and method parameters at runtime.

The `ParameterResolver` interface has three main implementations— `TestInfoParameterResolver`, `TestReporterParameterResolver`, and `RepetitionInfoParameterResolver`.

## The TestInfoParmeterResolver class
The `TestInfoParameterResolver` class provides an instance of `TestInfo`. The `TestInfo` interface is used to inject information about the current test, which includes the following:

- `Display Name` 
- `Class` 
- `Method`
- `Tags` 

This interface can be used in different types of tests with annotations—`@Test`, `@ParameterizedTest`, `@RepeatedTest`, and `@TestFactory`.

It is also used for life cycle callback methods with annotations—`@BeforeEach`, `@AfterEach`, `@BeforeAll`, and `@AfterAll`.

In the JUnit 4 API, `TestInfo` is a drop-in replacement for the `TestName` rule from JUnit 4.

## Example

The following code demonstrates the use of `TestInfo` as the constructor and method parameter.







In previous `JUnit` versions, the constructors and methods in the tests did not have parameters. With `Jupiter`, it’s possible to define the constructor and method parameters. This enables `dependency injection` for our tests.

`Jupiter` provides the interface, `ParameterResolver`, which helps an API resolve the constructor and method parameters at runtime.

The `ParameterResolver` interface has three main implementations— `TestInfoParameterResolver`, `TestReporterParameterResolver`, and `RepetitionInfoParameterResolver`.

# The TestInfoParmeterResolver class
The `TestInfoParameterResolver` class provides an instance of `TestInfo`. The `TestInfo` interface is used to inject information about the current test, which includes the following:

- `Display Name` 
- `Class` 
- `Method`
- `Tags` 

This interface can be used in different types of tests with annotations—`@Test`, `@ParameterizedTest`, `@RepeatedTest`, and `@TestFactory`.

It is also used for life cycle callback methods with annotations—`@BeforeEach`, `@AfterEach`, `@BeforeAll`, and `@AfterAll`.

In the JUnit 4 API, `TestInfo` is a drop-in replacement for the `TestName` rule from JUnit 4.

# Example

The following code demonstrates the use of `TestInfo` as the constructor and method parameter.







Understand the use of dependency injection in JUnit 5 with the TestInfoParameterResolver.

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

Using the TestInfoParameterResolver Class