Add a testcontainers section in the reference docs

Closes gh-20734

Author: mbhave

spring-boot-project/spring-boot-docs/src/docs/asciidoc/howto.adoc

@@ -2947,3 +2947,48 @@ The following example shows how to do so in Gradle:
 		// ...
 	}
 ----
+
+
+
+[[howto-testcontainers]]
+===  Use TestContainers for integration testing
+The https://www.testcontainers.org/[TestContainers] library provides a way to manage services running inside Docker containers.
+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 etc.
+TestContainers can be used in a Spring Boot test as follows:
+
+[source,java,indent=0,subs="verbatim,quotes,attributes"]
+----
+@SpringBootTest
+@Testcontainers
+class ExampleIntegrationTests {
+
+    @Container
+    static Neo4jContainer<?> neo4j = new Neo4jContainer<>();
+
+}
+----
+
+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 using details from the running container, such as container IP or port.
+
+This can be done with a static `@DynamicPropertySource` method that allows adding adding dynamic property values to the Spring Environment.
+
+[source,java,indent=0,subs="verbatim,quotes,attributes"]
+----
+@SpringBootTest
+@Testcontainers
+class ExampleIntegrationTests {
+
+    @Container
+    static Neo4jContainer<?> neo4j = new Neo4jContainer<>();
+
+    @DynamicPropertySource
+    static void neo4jProperties(DynamicPropertyRegistry registry) {
+        registry.add("spring.data.neo4j.uri", neo4j::getBoltUrl);
+    }
+
+}
+----
+
+The above configuration allows Neo4j-related beans in the application to communicate with Neo4j running inside the Testcontainers-managed Docker container.