Added unit test case

Author: Kamalesh-Periyasamy

maui/tests/Syncfusion.Maui.Toolkit.UnitTest/Buttons/SfButtonUnitTests.cs

@@ -699,6 +699,32 @@ public void CalculateWidth_ShouldReturnWidth(double width, double expectedValue)
 			Assert.Equal(expectedValue, actualValue);
 		}
 
+		[Theory]
+		[InlineData(150, 142, "SampleImage1.png", Alignment.Left)]
+		[InlineData(150, 108, "SampleImage1.png", Alignment.Right)]
+		[InlineData(180, 164, "SampleImage1.png", Alignment.Top)]
+		[InlineData(250, 234, "SampleImage1.png", Alignment.Bottom)]
+		[InlineData(200, 184, "SampleImage1.png", null)]
+		public void CalculateAvailableTextWidth_ShouldReturnExpectedWidth(double width, double expectedValue, string imagePath, Alignment? alignment = null)
+		{
+			// Arrange
+			var button = new SfButton();
+			button.ImageSource = ImageSource.FromFile(imagePath);
+
+			if (alignment != null)
+			{
+				button.ShowIcon = true;
+				button.ImageAlignment = (Alignment)alignment;
+			}
+
+			// Set up as needed
+			button.Padding = new Thickness(4, 4, 4, 4);
+
+			var actualValue = InvokePrivateMethod(button, "CalculateAvailableTextWidth", width);
+
+			Assert.Equal(expectedValue, actualValue);
+		}
+
 		[Theory]
 		[InlineData(true, false, false, false, "#000000")] 
 		[InlineData(true, true, false, false, "#FF0000")]