diff --git a/src/Microsoft.DotNet.Wpf/tests/UnitTests/PresentationCore.Tests/System/Windows/TextDecorationCollectionConverter.Tests.cs b/src/Microsoft.DotNet.Wpf/tests/UnitTests/PresentationCore.Tests/System/Windows/TextDecorationCollectionConverter.Tests.cs
new file mode 100644
index 00000000000..177eae7298b
--- /dev/null
+++ b/src/Microsoft.DotNet.Wpf/tests/UnitTests/PresentationCore.Tests/System/Windows/TextDecorationCollectionConverter.Tests.cs
@@ -0,0 +1,265 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.ComponentModel.Design.Serialization;
+using System.Globalization;
+
+namespace System.Windows;
+
+public class TextDecorationCollectionConverterTests
+{
+    [Theory]
+    // Only valid type
+    [InlineData(true, typeof(string))]
+    // Invalid types
+    [InlineData(false, typeof(TextDecorationCollection))]
+    [InlineData(false, typeof(IEnumerable<TextDecoration>))]
+    [InlineData(false, typeof(InstanceDescriptor))]
+    public void CanConvertFrom_ReturnsExpected(bool expected, Type sourceType)
+    {
+        TextDecorationCollectionConverter converter = new();
+
+        Assert.Equal(expected, converter.CanConvertFrom(sourceType));
+    }
+
+    [Theory]
+    // Only valid type
+    [InlineData(true, typeof(InstanceDescriptor))]
+    // Invalid types
+    [InlineData(false, typeof(TextDecorationCollection))]
+    [InlineData(false, typeof(IEnumerable<TextDecoration>))]
+    [InlineData(false, typeof(string))]
+    public void CanConvertTo_ReturnsExpected(bool expected, Type destinationType)
+    {
+        TextDecorationCollectionConverter converter = new();
+
+        Assert.Equal(expected, converter.CanConvertTo(destinationType));
+    }
+
+    [Theory]
+    [MemberData(nameof(ConvertFrom_ReturnsExpected_Data))]
+    public void ConvertFrom_ReturnsExpected(TextDecorationCollection expected, CultureInfo cultureInfo, string text)
+    {
+        TextDecorationCollectionConverter converter = new();
+
+        TextDecorationCollection? converted = (TextDecorationCollection?)converter.ConvertFrom(null, cultureInfo, text);
+
+        // Check count
+        Assert.NotNull(converted);
+        Assert.Equal(expected.Count, converted.Count);
+
+        // We require the order to be exact as well
+        for (int i = 0; i < expected.Count; i++)
+        {
+            Assert.Equal(expected[i], converted[i]);
+        }
+    }
+
+    public static IEnumerable<object?[]> ConvertFrom_ReturnsExpected_Data
+    {
+        get
+        {
+            // "None" returns no items
+            yield return new object[] { new TextDecorationCollection(), CultureInfo.InvariantCulture, string.Empty };
+            yield return new object[] { new TextDecorationCollection(), CultureInfo.InvariantCulture, "          " };
+            yield return new object[] { new TextDecorationCollection(), CultureInfo.InvariantCulture, "None" };
+            yield return new object[] { new TextDecorationCollection(), CultureInfo.InvariantCulture, "      None     " };
+
+            yield return new object[] { new TextDecorationCollection(), new CultureInfo("ru-RU"), string.Empty };
+            yield return new object[] { new TextDecorationCollection(), new CultureInfo("no-NO"), "          " };
+            yield return new object[] { new TextDecorationCollection(), new CultureInfo("no-NO"), "None" };
+            yield return new object[] { new TextDecorationCollection(), new CultureInfo("ru-RU"), "      None     " };
+
+            // Order matters here
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Strikethrough[0]]), new CultureInfo("no-NO"), "Strikethrough" };
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Strikethrough[0]]), new CultureInfo("ru-RU"), "Strikethrough           " };
+
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Underline[0], TextDecorations.Baseline[0]]),
+                                        new CultureInfo("no-NO"),
+                                        "Underline, Baseline" };
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Strikethrough[0], TextDecorations.Underline[0], TextDecorations.Baseline[0]]),
+                                        new CultureInfo("ru-RU"),
+                                        "  Strikethrough   ,Underline, Baseline " };
+
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Strikethrough[0], TextDecorations.Underline[0],
+                                                                      TextDecorations.Baseline[0], TextDecorations.OverLine[0]]),
+                                                                      new CultureInfo("fr-FR"), "  Strikethrough   ,Underline, Baseline        , Overline             " };
+
+        }
+    }
+
+    [Theory]
+    // Starts with a separator
+    [InlineData(",  Strikethrough   ,Underline, Baseline ")]
+    // Ends with a separator
+    [InlineData(" Strikethrough   ,Underline, Baseline, Overline, ")]
+    // Duplicate item (must be unique)
+    [InlineData("  Strikethrough  , Strikethrough, ,Underline, Baseline ")]
+    [InlineData(" Underline, Underline ")]
+    // None must be specified alone
+    [InlineData("None,  Strikethrough   ,Underline, Baseline ")]
+    [InlineData("None,  Strikethrough   ,Underline, Baseline, Overline ")]
+    // Invalid decoration at the end
+    [InlineData(" Strikethrough   ,Underline, Baseline, Overline, x ")]
+    // Invalid decoration
+    [InlineData(" Noneee ")]
+    // Invalid data type
+    [InlineData(double.PositiveInfinity)]
+    [InlineData(1554554)]
+    [InlineData(125.4d)]
+    public void ConvertFrom_ThrowsArgumentException(object? source)
+    {
+        TextDecorationCollectionConverter converter = new();
+
+        Assert.Throws<ArgumentException>(() => converter.ConvertFrom(null, null, source));
+    }
+
+    [Theory]
+    [MemberData(nameof(ConvertFromString_ReturnsExpected_Data))]
+    public void ConvertFromString_ReturnsExpected(TextDecorationCollection expected, string text)
+    {
+        TextDecorationCollection converted = TextDecorationCollectionConverter.ConvertFromString(text);
+
+        // Check count
+        Assert.Equal(expected.Count, converted.Count);
+
+        // We require the order to be exact as well
+        for (int i = 0; i < expected.Count; i++)
+        {
+            Assert.Equal(expected[i], converted[i]);
+        }
+    }
+
+    public static IEnumerable<object?[]> ConvertFromString_ReturnsExpected_Data
+    {
+        get
+        {
+            // "None" returns no items
+            yield return new object[] { new TextDecorationCollection(), string.Empty };
+            yield return new object[] { new TextDecorationCollection(), "          " };
+            yield return new object[] { new TextDecorationCollection(), "None" };
+            yield return new object[] { new TextDecorationCollection(), "      None     " };
+
+            // Order matters here
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Strikethrough[0]]), "Strikethrough" };
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Strikethrough[0]]), "Strikethrough           " };
+
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Underline[0], TextDecorations.Baseline[0]]), "Underline, Baseline" };
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Strikethrough[0], TextDecorations.Underline[0], TextDecorations.Baseline[0]]),
+                                                                     "  Strikethrough   ,Underline, Baseline " };
+
+            yield return new object[] { new TextDecorationCollection([TextDecorations.Strikethrough[0], TextDecorations.Underline[0],
+                                                                      TextDecorations.Baseline[0], TextDecorations.OverLine[0]]),
+                                                                     "  Strikethrough   ,Underline, Baseline        , Overline             " };
+
+        }
+    }
+
+    [Fact]
+    public void ConvertFromString_NullValue_ReturnsNull()
+    {
+        // null is simply null (NOTE: This differs from instance method ConvertFrom, that will throw on null value)
+        TextDecorationCollection? converted = TextDecorationCollectionConverter.ConvertFromString(null);
+
+        Assert.Null(converted);
+    }
+
+    [Theory]
+    // Starts with a separator
+    [InlineData(",  Strikethrough   ,Underline, Baseline ")]
+    // Ends with a separator
+    [InlineData(" Strikethrough   ,Underline, Baseline, Overline, ")]
+    // Duplicate item (must be unique)
+    [InlineData("  Strikethrough  , Strikethrough, ,Underline, Baseline ")]
+    [InlineData(" Underline, Underline ")]
+    // None must be specified alone
+    [InlineData("None,  Strikethrough   ,Underline, Baseline ")]
+    [InlineData("None,  Strikethrough   ,Underline, Baseline, Overline ")]
+    // Invalid decoration at the end
+    [InlineData(" Strikethrough   ,Underline, Baseline, Overline, x ")]
+    // Invalid decoration
+    [InlineData(" Noneee ")]
+    public void ConvertFromString_ThrowsArgumentException(string text)
+    {
+        Assert.Throws<ArgumentException>(() => TextDecorationCollectionConverter.ConvertFromString(text));
+    }
+
+    [Theory]
+    [MemberData(nameof(ConvertTo_ReturnsExpected_Data))]
+    public void ConvertTo_ReturnsExpected(TextDecorationCollection expected, object? value, Type destinationType)
+    {
+        TextDecorationCollectionConverter converter = new();
+
+        InstanceDescriptor? result = (InstanceDescriptor?)converter.ConvertTo(null, null, value, destinationType);
+
+        Assert.NotNull(result);
+
+        // Create instance using the InstanceDescriptor
+        TextDecorationCollection? actual = (TextDecorationCollection?)result.Invoke();
+
+        // Check instance
+        Assert.NotNull(actual);
+        Assert.Equal(expected.Count, actual.Count);
+
+        // We require the order to be exact as well
+        for (int i = 0; i < expected.Count; i++)
+        {
+            Assert.Equal(expected[i], actual[i]);
+        }
+    }
+
+    public static IEnumerable<object[]> ConvertTo_ReturnsExpected_Data
+    {
+        get
+        {
+            // Single decoration
+            yield return new object[] { new TextDecorationCollection(new TextDecoration[1] { TextDecorations.Underline[0] }),
+                                        new TextDecorationCollection(new TextDecoration[1] { TextDecorations.Underline[0] }),
+                                        typeof(InstanceDescriptor) };
+
+            // Multiple decorations
+            yield return new object[] { new TextDecorationCollection(new TextDecoration[3] { TextDecorations.Underline[0], TextDecorations.OverLine[0], TextDecorations.Baseline[0] }),
+                                        new TextDecorationCollection(new TextDecoration[3] { TextDecorations.Underline[0], TextDecorations.OverLine[0], TextDecorations.Baseline[0] }),
+                                        typeof(InstanceDescriptor) };
+
+            // Source value just needs to be IEnumerable<TextDecoration>
+
+            // T[]
+            yield return new object[] { new TextDecorationCollection(new TextDecoration[3] { TextDecorations.Underline[0], TextDecorations.OverLine[0], TextDecorations.Baseline[0] }),
+                                        new TextDecoration[3] { TextDecorations.Underline[0], TextDecorations.OverLine[0], TextDecorations.Baseline[0] }, typeof(InstanceDescriptor) };
+
+            // List<T>
+            yield return new object[] { new TextDecorationCollection(new TextDecoration[3] { TextDecorations.Underline[0], TextDecorations.OverLine[0], TextDecorations.Baseline[0] }),
+                                        new List<TextDecoration> { TextDecorations.Underline[0], TextDecorations.OverLine[0], TextDecorations.Baseline[0] }, typeof(InstanceDescriptor) };
+        }
+    }
+
+    [Theory]
+    [MemberData(nameof(ConvertTo_ThrowsArgumentNullException_Data))]
+    public void ConvertTo_ThrowsArgumentNullException(object value, Type destinationType)
+    {
+        TextDecorationCollectionConverter converter = new();
+
+        Assert.Throws<ArgumentNullException>(() => converter.ConvertTo(null, null, value, destinationType));
+    }
+
+    public static IEnumerable<object?[]> ConvertTo_ThrowsArgumentNullException_Data
+    {
+        get
+        {
+            // null value and destinationType
+            yield return new object?[] { null, null };
+            // supported value, null destinationType
+            yield return new object?[] { new TextDecorationCollection(), null };
+        }
+    }
+
+    [Fact]
+    public void ConvertTo_ThrowsNotSupportedException()
+    {
+        TextDecorationCollectionConverter converter = new();
+
+        // supported value, bad destinationType
+        Assert.Throws<NotSupportedException>(() => converter.ConvertTo(null, null, new TextDecorationCollection(), typeof(TextDecorationCollection)));
+    }
+}