Restore proxying of @Bean methods in @TestConfiguration

See gh-18675

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/context/TestConfiguration.java

@@ -23,6 +23,7 @@ import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 
 import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.annotation.AliasFor;
 
@@ -51,4 +52,29 @@ public @interface TestConfiguration {
 	@AliasFor(annotation = Configuration.class)
 	String value() default "";
 
+	/**
+	 * Specify whether {@link Bean @Bean} methods should get proxied in order to enforce
+	 * bean lifecycle behavior, e.g. to return shared singleton bean instances even in
+	 * case of direct {@code @Bean} method calls in user code. This feature requires
+	 * method interception, implemented through a runtime-generated CGLIB subclass which
+	 * comes with limitations such as the configuration class and its methods not being
+	 * allowed to declare {@code final}.
+	 * <p>
+	 * The default is {@code true}, allowing for 'inter-bean references' within the
+	 * configuration class as well as for external calls to this configuration's
+	 * {@code @Bean} methods, e.g. from another configuration class. If this is not needed
+	 * since each of this particular configuration's {@code @Bean} methods is
+	 * self-contained and designed as a plain factory method for container use, switch
+	 * this flag to {@code false} in order to avoid CGLIB subclass processing.
+	 * <p>
+	 * Turning off bean method interception effectively processes {@code @Bean} methods
+	 * individually like when declared on non-{@code @Configuration} classes, a.k.a.
+	 * "@Bean Lite Mode" (see {@link Bean @Bean's javadoc}). It is therefore behaviorally
+	 * equivalent to removing the {@code @Configuration} stereotype.
+	 * @since 2.2.1
+	 * @return whether to proxy {@code @Bean} methods
+	 */
+	@AliasFor(annotation = Configuration.class)
+	boolean proxyBeanMethods() default true;
+
 }