Add LaplacianKernelFactory tests

tests/ImageSharp.Tests/Processing/Convolution/Processors/LaplacianKernelFactoryTests.cs

@@ -0,0 +1,68 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using SixLabors.ImageSharp.Primitives;
+using SixLabors.ImageSharp.Processing.Convolution.Processors;
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests.Processing.Convolution.Processors
+{
+    public class LaplacianKernelFactoryTests
+    {
+        private static readonly ApproximateFloatComparer ApproximateComparer = new ApproximateFloatComparer(0.0001F);
+
+        private static readonly DenseMatrix<float> Expected3x3Matrix = new DenseMatrix<float>(
+            new float[,]
+                {
+                    { -1, -1, -1 },
+                    { -1,  8, -1 },
+                    { -1, -1, -1 }
+                });
+
+        private static readonly DenseMatrix<float> Expected5x5Matrix = new DenseMatrix<float>(
+            new float[,]
+                {
+                    { -1, -1, -1,-1, -1 },
+                    { -1, -1, -1,-1, -1 },
+                    { -1, -1, 24,-1, -1 },
+                    { -1, -1, -1,-1, -1 },
+                    { -1, -1, -1,-1, -1 }
+                });
+
+        [Fact]
+        public void LaplacianKernelFactoryOutOfRangeThrows()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() =>
+            {
+                LaplacianKernelFactory.CreateKernel(2);
+            });
+        }
+
+        [Fact]
+        public void LaplacianKernelFactoryCreatesCorrect3x3Matrix()
+        {
+            DenseMatrix<float> actual = LaplacianKernelFactory.CreateKernel(3);
+            for (int y = 0; y < actual.Rows; y++)
+            {
+                for (int x = 0; x < actual.Columns; x++)
+                {
+                    Assert.Equal(Expected3x3Matrix[y, x], actual[y, x], ApproximateComparer);
+                }
+            }
+        }
+
+        [Fact]
+        public void LaplacianKernelFactoryCreatesCorrect5x5Matrix()
+        {
+            DenseMatrix<float> actual = LaplacianKernelFactory.CreateKernel(5);
+            for (int y = 0; y < actual.Rows; y++)
+            {
+                for (int x = 0; x < actual.Columns; x++)
+                {
+                    Assert.Equal(Expected5x5Matrix[y, x], actual[y, x], ApproximateComparer);
+                }
+            }
+        }
+    }
+}