Document naming convention for custom test-scoped starters

See gh-49014

Signed-off-by: Stefano Cordio <stefano.cordio@gmail.com>

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/features/developing-auto-configuration.adoc

@@ -249,6 +249,8 @@ At the same time, others can rely only on the `autoconfigure` module and craft t
 
 If the auto-configuration is relatively straightforward and does not have optional features, merging the two modules in the starter is definitely an option.
 
+When testing "acme" features, you may need test-specific auto-configuration, for example, to replace external dependencies with in-memory alternatives.
+A separate test-scoped starter can be created for this purpose, following the same principles.
 
 
 [[features.developing-auto-configuration.custom-starter.naming]]
@@ -262,6 +264,7 @@ As a rule of thumb, you should name a combined module after the starter.
 For example, assume that you are creating a starter for "acme" and that you name the auto-configure module `acme-spring-boot` and the starter `acme-spring-boot-starter`.
 If you only have one module that combines the two, name it `acme-spring-boot-starter`.
 
+If "acme" also has a test-scoped starter, name it `acme-spring-boot-starter-test`.
 
 
 [[features.developing-auto-configuration.custom-starter.configuration-keys]]