Document @DynamicPropertySource support in the reference manual

Closes gh-24540

Author: sbrannen

src/docs/asciidoc/testing.adoc

@@ -3947,7 +3947,6 @@ to define properties in both a subclass and its superclass by using inline prope
 		// ...
 	}
 ----
-
 [source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
 .Kotlin
 ----
@@ -3964,6 +3963,54 @@ to define properties in both a subclass and its superclass by using inline prope
 	}
 ----
 
+[[testcontext-ctx-management-dynamic-property-sources]]
+===== Context Configuration with Dynamic Property Sources
+
+As of Spring Framework 5.2.5, the TestContext framework provides support for _dynamic_
+property sources via the `@DynamicPropertySource` annotation. This annotation can be used
+in integration tests that need to add properties with dynamic values to the set of
+`PropertySources` in the `Environment` for the `ApplicationContext` loaded for the
+integration test.
+
+NOTE: The `@DynamicPropertySource` annotation and its supporting infrastructure were
+originally designed to allow properties from
+https://www.testcontainers.org/[Testcontainers] based tests to be exposed easily to
+Spring integration tests. However, this feature may also be used with any form of
+external resource whose lifecycle is maintained outside the test's `ApplicationContext`.
+
+In contrast to the <<testcontext-ctx-management-property-sources,`@TestPropertySource`>>
+annotation that is applied at the class level, `@DynamicPropertySource` must be applied
+to a `static` method that accepts a single `DynamicPropertyRegistry` argument which is
+used to add _name-value_ pairs to the `Environment`. Values are dynamic and provided via
+a `Supplier` which is only invoked when the property is resolved. Typically, method
+references are used to supply values, as can be seen in the following example which uses
+the Testcontainers project to manage a Redis container outside of the Spring
+`ApplicationContext`. The IP address and port of the managed Redis container are made
+available to components within the test's `ApplicationContext` via the `redis.host` and
+`redis.port` properties. These properties can be injected into Spring-managed components
+via `@Value("${redis.host}")` and `@Value("${redis.port}")`, respectively.
+
+[source,java,indent=0,subs="verbatim,quotes",role="primary"]
+.Java
+----
+	@SpringJUnitConfig(/* ... */)
+	@Testcontainers
+	class ExampleIntegrationTests {
+
+		@Container
+		static RedisContainer redis = new RedisContainer();
+
+		@DynamicPropertySource
+		static void redisProperties(DynamicPropertyRegistry registry) {
+			registry.add("redis.host", redis::getContainerIpAddress);
+			registry.add("redis.port", redis::getMappedPort);
+		}
+
+		// tests ...
+
+	}
+----
+
 [[testcontext-ctx-management-web]]
 ===== Loading a `WebApplicationContext`