Add MongoConfigurationContributor tests and document it better (#76)

Author: stIncMale

Diff for: src/main/java/com/mongodb/hibernate/service/spi/MongoConfigurationContributor.java

@@ -18,6 +18,7 @@
 
 import com.mongodb.hibernate.cfg.MongoConfigurator;
 import java.util.Map;
+import org.hibernate.boot.registry.StandardServiceRegistry;
 import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
 import org.hibernate.service.Service;
 import org.hibernate.service.spi.Configurable;
@@ -53,7 +54,9 @@
 public interface MongoConfigurationContributor extends Service {
 
     /**
-     * Configures the MongoDB extension of Hibernate ORM.
+     * Configures the MongoDB extension of Hibernate ORM. This method is called once per instance of
+     * {@link StandardServiceRegistry} that has this {@link MongoConfigurationContributor}
+     * {@linkplain StandardServiceRegistryBuilder#addService(Class, Service) added}.
      *
      * @param configurator The {@link MongoConfigurator} pre-configured with {@linkplain Configurable#configure(Map)
      *     configuration properties}.

Diff for: src/test/java/com/mongodb/hibernate/internal/service/StandardServiceRegistryScopedStateTests.java

@@ -16,16 +16,21 @@
 
 package com.mongodb.hibernate.internal.service;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotSame;
 
 import com.mongodb.hibernate.internal.extension.service.StandardServiceRegistryScopedState;
+import com.mongodb.hibernate.service.spi.MongoConfigurationContributor;
+import java.util.ArrayList;
+import org.hibernate.boot.MetadataSources;
 import org.hibernate.boot.registry.BootstrapServiceRegistryBuilder;
 import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
+import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 
 class StandardServiceRegistryScopedStateTests {
     @Test
-    void differentStandardServiceRegistriesHaveDifferentStateInstances() {
+    void differentStandardServiceRegistriesHaveDifferentStates() {
         try (var bootstrapServiceRegistry = new BootstrapServiceRegistryBuilder().build()) {
             var standardServiceRegistryBuilder = new StandardServiceRegistryBuilder(bootstrapServiceRegistry);
             try (var standardServiceRegistry1 = standardServiceRegistryBuilder.build();
@@ -36,4 +41,29 @@ void differentStandardServiceRegistriesHaveDifferentStateInstances() {
             }
         }
     }
+
+    @Test
+    @DisplayName(
+            "MongoConfigurationContributor is called once per StandardServiceRegistry, different MongoConfigurator instances passed")
+    @SuppressWarnings("try")
+    void mongoConfigurationContributorInvocationsAndMongoConfiguratorInstances() {
+        try (var bootstrapServiceRegistry = new BootstrapServiceRegistryBuilder().build()) {
+            var mongoConfigurators = new ArrayList<>();
+            MongoConfigurationContributor mongoConfigurationContributor = mongoConfigurators::add;
+            var standardServiceRegistryBuilder = new StandardServiceRegistryBuilder(bootstrapServiceRegistry)
+                    .addService(MongoConfigurationContributor.class, mongoConfigurationContributor);
+            var metadataSources = new MetadataSources();
+            try (var standardServiceRegistry1 = standardServiceRegistryBuilder.build();
+                    var sessionFactory1 = metadataSources
+                            .buildMetadata(standardServiceRegistry1)
+                            .buildSessionFactory();
+                    var standardServiceRegistry2 = standardServiceRegistryBuilder.build();
+                    var sessionFactory2 = metadataSources
+                            .buildMetadata(standardServiceRegistry2)
+                            .buildSessionFactory()) {
+                assertEquals(2, mongoConfigurators.size());
+                assertNotSame(mongoConfigurators.get(0), mongoConfigurators.get(1));
+            }
+        }
+    }
 }