NH-3807 - Fix tests related to WeakReference and .NET Core changes.

.NET Core extended the lifetime of some temporary variables and that affected how the tests were constructed to test WeakReference as used in WeakHashtable and WeakRefWrapper.  Making sure the temporary variables are short lived in a NoInlining method is the solution.

Author: ngbrown

src/NHibernate.Test/UtilityTest/WeakHashtableFixture.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections;
-using System.IO;
-using System.Runtime.Serialization.Formatters.Binary;
+using System.Runtime.CompilerServices;
 
 using NHibernate.Util;
 using NUnit.Framework;
@@ -11,11 +10,30 @@ namespace NHibernate.Test.UtilityTest
 	[TestFixture]
 	public class WeakHashtableFixture
 	{
-		protected WeakHashtable Create()
+		private static WeakHashtable Create()
 		{
 			return new WeakHashtable();
 		}
 
+		// NoInlining to keep temporary variables' lifetime from being extended.
+		[MethodImpl(MethodImplOptions.NoInlining)]
+		private static WeakHashtable CreateWithTwoObjects()
+		{
+			var table = Create();
+
+			table[new object()] = new object();
+			table[new object()] = new object();
+
+			return table;
+		}
+
+		[MethodImpl(MethodImplOptions.NoInlining)]
+		private static WeakRefWrapper CreateWeakRefWrapper()
+		{
+			object obj = new object();
+			return new WeakRefWrapper(obj);
+		}
+
 		[Test]
 		public void Basic()
 		{
@@ -33,10 +51,8 @@ public void Basic()
 		[Test]
 		public void WeakReferenceGetsFreedButHashCodeRemainsConstant()
 		{
-			object obj = new object();
-			WeakRefWrapper wr = new WeakRefWrapper(obj);
+			WeakRefWrapper wr = CreateWeakRefWrapper();
 			int hashCode = wr.GetHashCode();
-			obj = null;
 
 			GC.Collect();
 
@@ -48,10 +64,7 @@ public void WeakReferenceGetsFreedButHashCodeRemainsConstant()
 		[Test]
 		public void Scavenging()
 		{
-			WeakHashtable table = Create();
-
-			table[new object()] = new object();
-			table[new object()] = new object();
+			WeakHashtable table = CreateWithTwoObjects();
 
 			GC.Collect();
 			table.Scavenge();
@@ -62,10 +75,7 @@ public void Scavenging()
 		[Test]
 		public void IterationAfterGC()
 		{
-			WeakHashtable table = Create();
-
-			table[new object()] = new object();
-			table[new object()] = new object();
+			WeakHashtable table = CreateWithTwoObjects();
 
 			GC.Collect();