Added tests for out jpeg image size getter method

tests/ImageSharp.Tests/Formats/Jpg/SpectralConverterTests.cs

@@ -0,0 +1,79 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder;
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Jpg
+{
+    [Trait("Format", "Jpg")]
+    public class SpectralConverterTests
+    {
+        [Theory]
+        [InlineData(1, 1)]
+        [InlineData(800, 400)]
+        [InlineData(2354, 4847)]
+        public void CalculateResultingImageSize_Null_TargetSize(int width, int height)
+        {
+            Size inputSize = new(width, height);
+
+            Size outputSize = SpectralConverter.CalculateResultingImageSize(inputSize, null, out int blockPixelSize);
+
+            Assert.Equal(expected: 8, blockPixelSize);
+            Assert.Equal(inputSize, outputSize);
+        }
+
+        // Test for 'perfect' dimensions, i.e. dimensions divisible by 8, with exact scaled size match
+        [Theory]
+        [InlineData(800, 400, 800, 400, 8)]
+        [InlineData(800, 400, 400, 200, 4)]
+        [InlineData(800, 400, 200, 100, 2)]
+        [InlineData(800, 400, 100, 50, 1)]
+        public void CalculateResultingImageSize_Perfect_Dimensions_Exact_Match(int inW, int inH, int tW, int tH, int expectedBlockSize)
+        {
+            Size inputSize = new(inW, inH);
+            Size targetSize = new(tW, tH);
+
+            Size outputSize = SpectralConverter.CalculateResultingImageSize(inputSize, targetSize, out int blockPixelSize);
+
+            Assert.Equal(expectedBlockSize, blockPixelSize);
+            Assert.Equal(outputSize, targetSize);
+        }
+
+        // Test for 'imperfect' dimensions, i.e. dimensions NOT divisible by 8, with exact scaled size match
+        [Theory]
+        [InlineData(7, 14, 7, 14, 8)]
+        [InlineData(7, 14, 4, 7, 4)]
+        [InlineData(7, 14, 2, 4, 2)]
+        [InlineData(7, 14, 1, 2, 1)]
+        public void CalculateResultingImageSize_Imperfect_Dimensions_Exact_Match(int inW, int inH, int tW, int tH, int expectedBlockSize)
+        {
+            Size inputSize = new(inW, inH);
+            Size targetSize = new(tW, tH);
+
+            Size outputSize = SpectralConverter.CalculateResultingImageSize(inputSize, targetSize, out int blockPixelSize);
+
+            Assert.Equal(expectedBlockSize, blockPixelSize);
+            Assert.Equal(outputSize, targetSize);
+        }
+
+        // Test for inexact target and output sizes match
+        [Theory]
+        [InlineData(7, 14, 4, 6, 4, 7, 4)]
+        [InlineData(7, 14, 1, 1, 1, 2, 1)]
+        [InlineData(800, 400, 999, 600, 800, 400, 8)]
+        [InlineData(800, 400, 390, 150, 400, 200, 4)]
+        [InlineData(804, 1198, 500, 800, 804, 1198, 8)]
+        public void CalculateResultingImageSize_Inexact_Target_Size(int inW, int inH, int tW, int tH, int exW, int exH, int expectedBlockSize)
+        {
+            Size inputSize = new(inW, inH);
+            Size targetSize = new(tW, tH);
+            Size expectedSize = new(exW, exH);
+
+            Size outputSize = SpectralConverter.CalculateResultingImageSize(inputSize, targetSize, out int blockPixelSize);
+
+            Assert.Equal(expectedBlockSize, blockPixelSize);
+            Assert.Equal(expectedSize, outputSize);
+        }
+    }
+}