feat(spanner): added unit test

Author: sagnghos

google-cloud-spanner/src/main/java/com/google/cloud/spanner/DatabaseId.java

@@ -94,7 +94,7 @@ public static DatabaseId of(String project, String instance, String database) {
     return new DatabaseId(new InstanceId(project, instance), database);
   }
 
-  /** Creates a {@code DatabaseId} given instance and database IDs. */
+  /** Creates a {@code DatabaseId} with "default" project, given instance and database IDs. */
   public static DatabaseId of(String instance, String database) {
     return new DatabaseId(new InstanceId("default", instance), database);
   }

google-cloud-spanner/src/test/java/com/google/cloud/spanner/SessionClientTests.java

@@ -20,6 +20,7 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.doNothing;
 import static org.mockito.Mockito.mock;
@@ -30,6 +31,7 @@
 import com.google.cloud.grpc.GrpcTransportOptions;
 import com.google.cloud.grpc.GrpcTransportOptions.ExecutorFactory;
 import com.google.cloud.spanner.SessionClient.SessionConsumer;
+import com.google.cloud.spanner.SessionClient.SessionId;
 import com.google.cloud.spanner.spi.v1.SpannerRpc;
 import com.google.cloud.spanner.spi.v1.SpannerRpc.Option;
 import com.google.common.collect.ImmutableMap;
@@ -503,4 +505,21 @@ public void onSessionCreateFailure(Throwable t, int createFailureForSessionCount
     }
     assertThat(returnedSessionCount.get()).isEqualTo(numSessions);
   }
+
+  @SuppressWarnings("unchecked")
+  @Test
+  public void testSessionNamePatterns() {
+    // Valid pattern for host session name
+    String host =
+        "projects/spanner-project/instances/spanner-instance/databases/test-db/sessions/abcd1234";
+    // Valid pattern for external host session name
+    String externalHost = "instances/default/databases/test-db/sessions/abcd1234";
+    try {
+      SessionId.of(host);
+      SessionId.of(externalHost);
+      // If no exceptions are thrown, the test will pass
+    } catch (IllegalArgumentException e) {
+      fail("Expected no exception to be thrown, but got: " + e.getMessage());
+    }
+  }
 }