#169 fixed NullReferenceException when comparing with a null Level

src/log4net.Tests/Core/LevelMapTest.cs

@@ -18,21 +18,20 @@
 #endregion
 
 using log4net.Core;
-using log4net.Tests.Layout;
 
 using NUnit.Framework;
 
 namespace log4net.Tests.Core
 {
   /// <summary>
-  /// Used for internal unit testing the <see cref="PatternLayoutTest"/> class.
+  /// Used for internal unit testing the <see cref="LevelMap"/> class.
   /// </summary>
-  /// <remarks>
-  /// Used for internal unit testing the <see cref="PatternLayoutTest"/> class.
-  /// </remarks>
   [TestFixture]
-  public class LevelMapTest
+  public sealed class LevelMapTest
   {
+    /// <summary>
+    /// Tests the creation of a <see cref="LevelMap"/> and calling its <see cref="LevelMap.Clear"/> method
+    /// </summary>
     [Test]
     public void LevelMapCreateClear()
     {

src/log4net.Tests/Core/LevelTest.cs

@@ -0,0 +1,73 @@
+#region Apache License
+//
+// Licensed to the Apache Software Foundation (ASF) under one or more 
+// contributor license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright ownership. 
+// The ASF licenses this file to you under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance with 
+// the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#endregion
+
+using System;
+using System.Runtime.CompilerServices;
+using log4net.Core;
+
+using NUnit.Framework;
+
+namespace log4net.Tests.Core
+{
+  /// <summary>
+  /// Used for internal unit testing the <see cref="Level"/> class.
+  /// </summary>
+  [TestFixture]
+  public sealed class LevelTest
+  {
+    /// <summary>
+    /// Tests the comparison between two <see cref="Level"/>s
+    /// </summary>
+    [Test]
+    public void LevelCompare()
+    {
+      Level? nullLevel = null;
+      int? nullInt = null;
+      Compare(nullInt, nullInt, nullLevel, nullLevel);
+      Compare(nullInt, Level.Verbose.Value, nullLevel, Level.Verbose);
+      Compare(Level.Verbose.Value, nullInt, Level.Verbose, nullLevel);
+      Compare(Level.Verbose.Value, Level.Verbose.Value, Level.Verbose, Level.Verbose);
+      Compare(Level.Debug.Value, Level.Verbose.Value, Level.Debug, Level.Verbose);
+    }
+
+    private static void Compare(int? leftInt, int? rightInt, Level? left, Level? right,
+      [CallerArgumentExpression(nameof(left))] string leftName = "",
+      [CallerArgumentExpression(nameof(right))] string rightName = "")
+    {
+      Assert.AreEqual(leftInt < rightInt, left < right, "{0} < {1}", leftName, rightName);
+      Assert.AreEqual(leftInt > rightInt, left > right, "{0} > {1}", leftName, rightName);
+      Assert.AreEqual(leftInt <= rightInt, left <= right, "{0} <= {1}", leftName, rightName);
+      Assert.AreEqual(leftInt >= rightInt, left >= right, "{0} >= {1}", leftName, rightName);
+      Assert.AreEqual(leftInt == rightInt, left == right, "{0} == {1}", leftName, rightName);
+      Assert.AreEqual(leftInt != rightInt, left != right, "{0} != {1}", leftName, rightName);
+      Assert.AreEqual(leftInt?.Equals(rightInt), left?.Equals(right), "{0}?.Equals({1})", leftName, rightName);
+      if (leftInt is not null)
+      {
+        if (rightInt is not null)
+        {
+          Assert.AreEqual(leftInt?.CompareTo(rightInt), left?.CompareTo(right!), "{0}?.CompareTo({1})", leftName, rightName);
+        }
+        else
+        {
+          Assert.Throws<ArgumentNullException>(() => left!.CompareTo(right!));
+        }
+      }
+    }
+  }
+}

src/log4net.Tests/log4net.Tests.csproj

@@ -13,6 +13,9 @@
     <!-- suppress analyzer mismatch warning -->
     <NoWarn>CS8032</NoWarn>
   </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="..\log4net\Diagnostics\CodeAnalysis\CallerArgumentExpressionAttribute.cs" Link="Diagnostics\CodeAnalysis\CallerArgumentExpressionAttribute.cs" />
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\log4net\log4net.csproj" />
   </ItemGroup>