Document methods of starting Testcontainer containers

Update the reference documentation to provide more details about the
three supported methods of starting Testcontainer containers.

See gh-44187

Signed-off-by: Vanio Begic <vanio.begic123@gmail.com>

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/testing/testcontainers.adoc

@@ -5,13 +5,89 @@ The https://www.testcontainers.org/[Testcontainers] library provides a way to ma
 It integrates with JUnit, allowing you to write a test class that can start up a container before any of the tests run.
 Testcontainers is especially useful for writing integration tests that talk to a real backend service such as MySQL, MongoDB, Cassandra and others.
 
+In following sections we will describe some of the methods you can use to integrate Testcontainers with your tests.
+
+
+
+[[testing.testcontainers.via-junit-extension]]
+== Using via @Testcontainers JUnit5 extension
+
+The Testcontainers provides JUnit5 extensions, which can be used to manage containers in your tests.
+The extension is activated by applying the `@Testcontainers` annotation from Testcontainers to your test class.
+
 Testcontainers can be used in a Spring Boot test as follows:
 
 include-code::vanilla/MyIntegrationTests[]
 
-This will start up a docker container running Neo4j (if Docker is running locally) before any of the tests are run.
+This will start up a Docker container running Neo4j (if Docker is running locally) before any of the tests are run.
 In most cases, you will need to configure the application to connect to the service running in the container.
 
+In this case the lifecycle of the container instance is managed by Testcontainers, as described in official documentation.
+
+
+[[testing.testcontainers.via-spring-beans]]
+== Using via Spring managed beans
+
+The containers provided by Testcontainers can be managed by Spring Boot as beans.
+This method of managing contains can be used in combination with javadoc:org.springframework.boot.testcontainers.service.connection.ServiceConnection[format=annotation].
+
+To use Testcontainer contains as Spring beans we need to create a configuration class declaring the container as bean:
+
+include-code::beandeclaration/BeanDeclarationConfig[]
+
+then we can start the container by importing the configuration class in the test class:
+
+include-code::beandeclaration/SpringTest[]
+
+
+[[testing.testcontainers.via-declaration-classes]]
+== Using via importing container declaration classes
+
+A common pattern with Testcontainers is to declare the Container instances as static fields in an interface.
+For example the following interface `MyInterface` declares two containers, one named `mongo` of type MongoDB and another named `neo` of type Neo4j:
+
+include-code::importcontainers/MyInterface[]
+
+When you have containers declared in this way, then you can have these containers managed by Spring Boot as beans.
+All that is needed to do that is adding javadoc:org.springframework.boot.testcontainers.context.ImportTestcontainers[format=annotation] to your configuration class as in:
+
+include-code::importcontainers/MyConfiguration[]
+
+TIP: Using interfaces for declaring contains helps with reuse.
+When containers are declared in an interface, this can be reused in your javadoc:org.springframework.context.annotation.Configuration[format=annotation] classes and in test classes.
+
+
+[[test.testcontainers.container-lifecycle]]
+== Lifecycle of managed containers
+
+If you have used the annotations and extensions provided by Testcontainers, then the lifecycle of container instances is managed by the Testcontainers.
+Please refer to the {url-testcontainres-java-doc}[Testcontainers official documentation] for the information about lifecycle of the containers, when managed by the Testcontainers.
+
+When the containers are managed by Spring as beans, then the lifecycle is clearly defined by Spring.
+The container beans are created and started before the beans of other types are created.
+This process ensures that any beans, which rely on functionality provided by the containers, can use those functionalities.
+
+The test containers can be started multiple times.
+Like any other beans the test containers are created and started once per application context managed by the TestContext Framework.
+For details about how TestContext framework manages the underlying application contexts and beans therein, please refer to the {url-spring-framework-docs}[official Spring documentation].
+
+The container beans are stopped after the destruction of beans of other types.
+This ensures that any beans depending on the functionalities provided by the containers are cleaned up first.
+
+TIP: When your application beans rely on functionality of containers, prefer configuring the containers as Spring beans.
+When containers are managed as Spring beans, then Spring framework ensures that upon start the container beans are started before any beans relying on them.
+On shutdown the application beans depending on container functionalities are cleaned up first, and only then are the containers shut down.
+
+NOTE: Having containers managed by Testcontainers instead of as Spring beans provides no guarantee of order in which beans and containers will shutdown.
+It can happen that containers are shutdown before the beans relying on container functionality are cleaned up.
+This can lead to exceptions being thrown by client beans due to loss of connection for example.
+
+The containers are stopped as part of the application shutdown process, managed by the TestContext framework.
+When the application context gets shutdown, the containers are shutdown as well.
+This usually happens after all tests using that specific cached application context have finished executing, but may happen earlier depending on the caching behavior configured in TestContext Framework.
+
+It is important to note that a single test container instance can be, and often is, retained across execution of tests from multiple test classes.
+
 
 
 [[testing.testcontainers.service-connections]]