build and testrunning fix

src/ImageSharp/Common/Memory/PixelDataPool{T}.cs

@@ -46,7 +46,8 @@ namespace ImageSharp
         /// <returns>The maxArrayLength value</returns>
         internal static int CalculateMaxArrayLength()
         {
-            if (typeof(IPixel).IsAssignableFrom(typeof(T)))
+            // ReSharper disable once SuspiciousTypeConversion.Global
+            if (default(T) is IPixel)
             {
                 const int MaximumExpectedImageSize = 16384;
                 return MaximumExpectedImageSize * MaximumExpectedImageSize;

tests/ImageSharp.Tests/Colors/BulkPixelOperationsTests.cs

@@ -9,22 +9,21 @@
     {
         public class Color : BulkPixelOperationsTests<ImageSharp.Color>
         {
-            // MemberData does not work without redeclaring the public field in the derived test class:
-            public static TheoryData<int> ArraySizesData = new TheoryData<int> { 7, 16, 1111 };
+            // For 4.6 test runner MemberData does not work without redeclaring the public field in the derived test class:
+            public static new TheoryData<int> ArraySizesData => new TheoryData<int> { 7, 16, 1111 };
         }
 
         public class Argb : BulkPixelOperationsTests<ImageSharp.Argb>
         {
-            // MemberData does not work without redeclaring the public field in the derived test class:
-            public static TheoryData<int> ArraySizesData = new TheoryData<int> { 7, 16, 1111 };
+            // For 4.6 test runner MemberData does not work without redeclaring the public field in the derived test class:
+            public static new TheoryData<int> ArraySizesData => new TheoryData<int> { 7, 16, 1111 };
         }
     }
 
     public abstract class BulkPixelOperationsTests<TColor>
         where TColor : struct, IPixel<TColor>
     {
-        // The field is private so it can be safely redeclared in inherited non-abstract test classes.
-        private static TheoryData<int> ArraySizesData = new TheoryData<int> { 7, 16, 1111 };
+        public static TheoryData<int> ArraySizesData => new TheoryData<int> { 7, 16, 1111 };
         
         [Theory]
         [MemberData(nameof(ArraySizesData))]