JUNIT JUPITER Engine framework in the Java class library

Junit Jupiter Engine framework is a powerful tool for writing and executing unit testing.As part of JUnit 5, it provides a flexible and scalability way to write and run the test code. Junit Jupiter Engine's technical principle is based on the following core concepts: 1. Extension Model: Junit Jupiter Engine provides flexible control of the test cycle through the extension model.Developers can customize extensions to achieve specific test behaviors, such as implementing TestInstancepostProcessor interfaces to process test instances, or implement the BeForeEachCallback interface to perform additional logic before each test method. 2. Annotation-Driven: Junit Jupiter Engine drives the test code by using the annotation.Developers can use a series of annotations to control the behavior of testing. For example, using @test annotations to identify a test method, and use @BeForeeach annotations to identify methods performed before each test method, etc. 3. Dynamic test discovery (Dynamic Test Discovery): Junit Jupiter Engine provides the ability to find dynamic testing, which can automatically find and execute specific annotation test methods at runtime.This provides developers with great flexibility, and can dynamically perform a set of test methods according to the conditions. Below is a simple example, demonstrate how to use Junit Jupiter Engine to write and execute unit test code: import org.junit.jupiter.api.Test; import static org.junit.jupiter.api.Assertions.*; class Calculator { int add(int a, int b) { return a + b; } } class CalculatorTest { @Test void testAdd() { Calculator calculator = new Calculator(); int result = calculator.add(2, 3); assertEquals(5, result); } } In the above example, we define a simple class called Calculator and a test class called CalculatorTest.Use the @teest annotation to identify a test method testadd.In this method, we created an instance of Calculator, called the ADD method, and used Asseretequals to assess to verify that the calculation results meet the expectations. Junit Jupiter Engine will automatically scan and execute the test method with @test annotation and output test results.By using the Junit Jupiter Engine framework, we can easily write various types of test code and better control the test behavior of the test.