Add tests, corners not working properly for some reason

UnitTests/TextEffects/New/GradientFillTests.cs

@@ -0,0 +1,111 @@
+namespace Terminal.Gui.TextEffects.Tests;
+
+public class GradientFillTests
+{
+    private Gradient _gradient;
+
+    public GradientFillTests ()
+    {
+        // Define the colors of the gradient stops
+        var stops = new List<Color>
+        {
+            Color.FromRgb(255, 0, 0),    // Red
+            Color.FromRgb(0, 0, 255)     // Blue
+        };
+
+        // Define the number of steps between each color
+        var steps = new List<int> { 10 }; // 10 steps between Red -> Blue
+
+        _gradient = new Gradient (stops, steps, loop: false);
+    }
+
+    [Fact]
+    public void TestGradientFillCorners ()
+    {
+        var area = new Rectangle (0, 0, 10, 10);
+        var gradientFill = new GradientFill (area, _gradient, Gradient.Direction.Diagonal);
+
+        // Test the corners
+        var topLeft = new Point (0, 0);
+        var topRight = new Point (area.Width - 1, 0);
+        var bottomLeft = new Point (0, area.Height - 1);
+        var bottomRight = new Point (area.Width - 1, area.Height - 1);
+
+        var topLeftColor = gradientFill.GetColor (topLeft);
+        var topRightColor = gradientFill.GetColor (topRight);
+        var bottomLeftColor = gradientFill.GetColor (bottomLeft);
+        var bottomRightColor = gradientFill.GetColor (bottomRight);
+
+        // Validate the colors at the corners
+        Assert.NotNull (topLeftColor);
+        Assert.NotNull (topRightColor);
+        Assert.NotNull (bottomLeftColor);
+        Assert.NotNull (bottomRightColor);
+
+        // Expected colors
+        var expectedTopLeftColor = new Terminal.Gui.Color (255, 0, 0); // Red
+        var expectedBottomRightColor = new Terminal.Gui.Color (0, 0, 255); // Blue
+
+        Assert.Equal (expectedTopLeftColor, topLeftColor);
+        Assert.Equal (expectedBottomRightColor, bottomRightColor);
+
+        // Additional checks can be added to verify the exact expected colors if known
+        Console.WriteLine ($"Top-left: {topLeftColor}");
+        Console.WriteLine ($"Top-right: {topRightColor}");
+        Console.WriteLine ($"Bottom-left: {bottomLeftColor}");
+        Console.WriteLine ($"Bottom-right: {bottomRightColor}");
+    }
+
+    [Fact]
+    public void TestGradientFillColorTransition ()
+    {
+        var area = new Rectangle (0, 0, 10, 10);
+        var gradientFill = new GradientFill (area, _gradient, Gradient.Direction.Diagonal);
+
+        for (int row = 0; row < area.Height; row++)
+        {
+            int previousRed = 255;
+            int previousBlue = 0;
+
+            for (int col = 0; col < area.Width; col++)
+            {
+                var point = new Point (col, row);
+                var color = gradientFill.GetColor (point);
+
+                // Ensure color is not null
+                Assert.NotNull (color);
+
+                // Check if the current color is 'more blue' and 'less red' as it goes right and down
+                Assert.True (color.R <= previousRed, $"Failed at ({col}, {row}): {color.R} > {previousRed}");
+                Assert.True (color.B >= previousBlue, $"Failed at ({col}, {row}): {color.B} < {previousBlue}");
+
+                // Update the previous color values for the next iteration
+                previousRed = color.R;
+                previousBlue = color.B;
+            }
+        }
+
+        for (int col = 0; col < area.Width; col++)
+        {
+            int previousRed = 255;
+            int previousBlue = 0;
+
+            for (int row = 0; row < area.Height; row++)
+            {
+                var point = new Point (col, row);
+                var color = gradientFill.GetColor (point);
+
+                // Ensure color is not null
+                Assert.NotNull (color);
+
+                // Check if the current color is 'more blue' and 'less red' as it goes right and down
+                Assert.True (color.R <= previousRed, $"Failed at ({col}, {row}): {color.R} > {previousRed}");
+                Assert.True (color.B >= previousBlue, $"Failed at ({col}, {row}): {color.B} < {previousBlue}");
+
+                // Update the previous color values for the next iteration
+                previousRed = color.R;
+                previousBlue = color.B;
+            }
+        }
+    }
+}