To isolate the test context for a specific part of a Spring Boot application, such as a web layer, you can use the @WebMvcTest annotation. It will configure a minimal Spring application context with only the components needed for testing the web layer.

Spring Boot supports reactive programming in conjunction with traditional MVC patterns by automatically adapting to the reactive or traditional approach based on the project's dependencies. It uses conditional configuration and auto-detection of libraries to determine whether to configure the application as reactive or traditional. This allows developers to seamlessly integrate reactive and non-reactive components within the same application, providing flexibility and compatibility with both programming models.

In Spring Boot, enabling "Lazy Initialization" can help in reducing the startup time of the application. Lazy initialization means that beans are created and initialized only when they are first requested, rather than eagerly during application startup. This can significantly improve startup performance, especially for large applications with many beans, as it avoids unnecessary upfront bean creation.

The @Configuration annotation is used to mark a class as a source of bean definitions. This means that any method annotated with @Bean within a class annotated with @Configuration will define a bean in the Spring context, allowing it to be injected into other components, services, etc. This is fundamental for creating the beans that make up the application context in a Spring application.

Option 3 is the best approach. Spring Security Test provides utilities for simulating authenticated users and roles, allowing you to test security constraints and access controls effectively.

WebFlux is a good choice when you need to handle a large number of concurrent connections with high responsiveness. It excels in scenarios where non-blocking, asynchronous processing is crucial to avoid thread blocking and efficiently utilize system resources. In contrast, the traditional blocking architecture is suitable for applications with lower concurrency and when synchronous processing is sufficient.

In JUnit, the @AfterClass annotation is used to indicate that a method should be executed after all tests in the current test class have been run. This is often used for cleanup tasks after running a suite of tests.

With @WebMvcTest, only the controllers and related components are typically loaded into the application context. This is useful for testing the web layer of your application in isolation without loading the entire context.

In Spring Boot, you can use the @BeforeEach annotation to specify actions that should be executed before testing each method. This is often used for setup actions before individual test cases.

In Spring Boot, to load only the web layer of an application during integration tests, you can use the @WebMvcTest annotation. It narrows down the scope of the context loaded for testing to just the web-related components.