Polish "Expose default RabbitMQ credentials in the metadata"

Closes gh-6863

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/amqp/RabbitAutoConfigurationTests.java

@@ -116,6 +116,20 @@ public class RabbitAutoConfigurationTests {
 				});
 	}
 
+	@Test
+	public void testDefaultConnectionFactoryConfiguration() {
+		this.contextRunner.withUserConfiguration(TestConfiguration.class)
+				.run((context) -> {
+					RabbitProperties properties = new RabbitProperties();
+					com.rabbitmq.client.ConnectionFactory rabbitConnectionFactory = getTargetConnectionFactory(
+							context);
+					assertThat(rabbitConnectionFactory.getUsername())
+							.isEqualTo(properties.getUsername());
+					assertThat(rabbitConnectionFactory.getPassword())
+							.isEqualTo(properties.getPassword());
+				});
+	}
+
 	@Test
 	public void testConnectionFactoryWithOverrides() {
 		this.contextRunner.withUserConfiguration(TestConfiguration.class)