Improve design type converters

src/Controls/src/Core.Design/EasingDesignTypeConverter.cs

@@ -6,6 +6,8 @@ public class EasingDesignTypeConverter : KnownValuesDesignTypeConverter
 		public EasingDesignTypeConverter()
 		{ }
 
+		protected override bool ExclusiveToKnownValues => true;
+
 		protected override string[] KnownValues
 			=> new string[]
 			{

src/Controls/src/Core.Design/KeyboardDesignTypeConverter.cs

@@ -11,6 +11,8 @@ public KeyboardDesignTypeConverter()
 		{
 		}
 
+		protected override bool ExclusiveToKnownValues => true;
+
 		protected override string[] KnownValues
 			=> new[]
 			{

src/Controls/src/Core.Design/LayoutOptionsDesignTypeConverter.cs

@@ -6,6 +6,8 @@ public LayoutOptionsDesignTypeConverter()
 		{
 		}
 
+		protected override bool ExclusiveToKnownValues => true;
+
 		protected override string[] KnownValues
 			=> new string[] { "Start", "Center", "End", "Fill", "StartAndExpand", "CenterAndExpand", "EndAndExpand", "FillAndExpand" };
 	}

src/Controls/tests/Core.Design.UnitTests/Controls.Core.Design.UnitTests.csproj

@@ -18,6 +18,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="ColorDesignTypeConverterTests.cs" />
+    <Compile Include="DesignTypeConverterTests.cs" />
     <Compile Include="GridLengthCollectionDesignTypeConverterTests.cs" />
     <Compile Include="GridLengthDesignTypeConverterTests.cs" />
   </ItemGroup>

src/Controls/tests/Core.Design.UnitTests/DesignTypeConverterTests.cs

@@ -0,0 +1,80 @@
+using Microsoft.Maui.Controls.Design;
+using Xunit;
+
+namespace Microsoft.Maui.Controls.Core.UnitTests
+{
+	public class DesignTypeConverterTests
+	{
+		[Theory]
+		[InlineData(null)]
+		[InlineData("")]
+		[InlineData("1")]
+		[InlineData("Sta")]
+		[InlineData("START")]
+		public void LayoutOptionsDesignTypeConverter_Invalid(string value)
+		{
+			LayoutOptionsDesignTypeConverter converter = new LayoutOptionsDesignTypeConverter();
+			bool actual = converter.IsValid(value);
+			Assert.False(actual);
+		}
+
+		[Theory]
+		[InlineData("Start")]
+		[InlineData("End")]
+		[InlineData("FillAndExpand")]
+		public void LayoutOptionsDesignTypeConverter_Valid(string value)
+		{
+			LayoutOptionsDesignTypeConverter converter = new LayoutOptionsDesignTypeConverter();
+			bool actual = converter.IsValid(value);
+			Assert.True(actual);
+		}
+
+		[Theory]
+		[InlineData(null)]
+		[InlineData("")]
+		[InlineData("1")]
+		[InlineData("Lin")]
+		[InlineData("LINEAR")]
+		public void EasingDesignTypeConverter_Invalid(string value)
+		{
+			EasingDesignTypeConverter converter = new EasingDesignTypeConverter();
+			bool actual = converter.IsValid(value);
+			Assert.False(actual);
+		}
+
+		[Theory]
+		[InlineData("Linear")]
+		[InlineData("BounceIn")]
+		[InlineData("CubicOut")]
+		public void EasingDesignTypeConverter_Valid(string value)
+		{
+			EasingDesignTypeConverter converter = new EasingDesignTypeConverter();
+			bool actual = converter.IsValid(value);
+			Assert.True(actual);
+		}
+
+		[Theory]
+		[InlineData(null)]
+		[InlineData("")]
+		[InlineData("1")]
+		[InlineData("Tele")]
+		[InlineData("TELEPHONE")]
+		public void KeyboardDesignTypeConverter_Invalid(string value)
+		{
+			KeyboardDesignTypeConverter converter = new KeyboardDesignTypeConverter();
+			bool actual = converter.IsValid(value);
+			Assert.False(actual);
+		}
+
+		[Theory]
+		[InlineData("Plain")]
+		[InlineData("Numeric")]
+		[InlineData("Telephone")]
+		public void KeyboardDesignTypeConverter_Valid(string value)
+		{
+			KeyboardDesignTypeConverter converter = new KeyboardDesignTypeConverter();
+			bool actual = converter.IsValid(value);
+			Assert.True(actual);
+		}
+	}
+}