Skip delete query if no polymorphic entities

Author: bahusoid

src/NHibernate.Test/TestCase.cs

@@ -3,6 +3,7 @@
 using System.Collections.Generic;
 using System.Data;
 using System.Data.Common;
+using System.Linq;
 using System.Reflection;
 using log4net;
 using NHibernate.Cfg;
@@ -230,13 +231,20 @@ private string GetCombinedFailureMessage(TestContext.ResultAdapter result, strin
 
 		protected virtual bool CheckDatabaseWasCleaned()
 		{
-			if (Sfi.GetAllClassMetadata().Count == 0)
+			var allClassMetadata = Sfi.GetAllClassMetadata();
+			if (allClassMetadata.Count == 0)
 			{
 				// Return early in the case of no mappings, also avoiding
 				// a warning when executing the HQL below.
 				return true;
 			}
 
+			var explicitPolymorphismEntities = allClassMetadata.Values.Where(x => x is NHibernate.Persister.Entity.IQueryable queryable && queryable.IsExplicitPolymorphism).ToArray();
+
+			//TODO: Maybe add explicit load query checks 
+			if (explicitPolymorphismEntities.Length == allClassMetadata.Count)
+				return true;
+
 			bool empty;
 			using (ISession s = OpenSession())
 			{