Add unit tests for length-unit conversion functionality

Source/QuestPDF.UnitTests/UnitConversionTests.cs

@@ -0,0 +1,25 @@
+using System.Collections.Generic;
+using NUnit.Framework;
+using QuestPDF.Infrastructure;
+
+namespace QuestPDF.UnitTests;
+
+[TestFixture]
+public class UnitConversionTests
+{
+    [TestCase(Unit.Point, 1f, 1f)]
+    [TestCase(Unit.Inch, 1f, 72f)]
+    [TestCase(Unit.Feet, 1f, 864f)]
+    [TestCase(Unit.Mil, 1000f, 72f)]
+    [TestCase(Unit.Centimetre, 2.54f, 72f)]      // 2.54 cm = 1 inch
+    [TestCase(Unit.Millimetre, 25.4f, 72f)]      // 25.4 mm = 1 inch
+    [TestCase(Unit.Meter, 0.0254f, 72f)]         // 0.0254 m = 1 inch
+    public void ToPoints_ConvertsCorrectly(Unit unit, float input, float expected)
+    {
+        var result = input.ToPoints(unit);
+        Assert.That(result, Is.EqualTo(expected));
+        
+        var result2 = (input * 2).ToPoints(unit);
+        Assert.That(result2, Is.EqualTo(expected * 2));
+    }
+}