diff --git a/src/System.Windows.Forms.Design.Editors/src/System/Windows/Forms/Design/FileNameEditor.cs b/src/System.Windows.Forms.Design.Editors/src/System/Windows/Forms/Design/FileNameEditor.cs
index ba9202bf67c..e6e75c10d09 100644
--- a/src/System.Windows.Forms.Design.Editors/src/System/Windows/Forms/Design/FileNameEditor.cs
+++ b/src/System.Windows.Forms.Design.Editors/src/System/Windows/Forms/Design/FileNameEditor.cs
@@ -2,49 +2,45 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System;
 using System.ComponentModel;
-using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Drawing.Design;
 
 namespace System.Windows.Forms.Design
 {
     /// <summary>>
-    ///         Provides an
-    ///         editor for filenames.
+    /// Provides an editor for filenames.
     /// </summary>
     [CLSCompliant(false)]
     public class FileNameEditor : UITypeEditor
     {
-        private OpenFileDialog openFileDialog;
+        private OpenFileDialog _openFileDialog;
 
         /// <summary>
-        ///     Edits the given object value using the editor style provided by
-        ///     GetEditorStyle.  A service provider is provided so that any
-        ///     required editing services can be obtained.
+        /// Edits the given object value using the editor style provided by GetEditorStyle.
+        /// A service provider is provided so that any required editing services can be obtained.
         /// </summary>
-        [SuppressMessage("Microsoft.Security", "CA2123:OverrideLinkDemandsShouldBeIdenticalToBase")]
         public override object EditValue(ITypeDescriptorContext context, IServiceProvider provider, object value)
         {
-            Debug.Assert(provider != null, "No service provider; we cannot edit the value");
             if (provider != null)
             {
-                IWindowsFormsEditorService edSvc =
-                    (IWindowsFormsEditorService)provider.GetService(typeof(IWindowsFormsEditorService));
-
-                Debug.Assert(edSvc != null, "No editor service; we cannot edit the value");
-                if (edSvc != null)
+                if (provider.GetService(typeof(IWindowsFormsEditorService)) is IWindowsFormsEditorService edSvc)
                 {
-                    if (openFileDialog == null)
+                    if (_openFileDialog == null)
                     {
-                        openFileDialog = new OpenFileDialog();
-                        InitializeDialog(openFileDialog);
+                        _openFileDialog = new OpenFileDialog();
+                        InitializeDialog(_openFileDialog);
                     }
 
-                    if (value is string) openFileDialog.FileName = (string)value;
+                    if (value is string stringValue)
+                    {
+                        _openFileDialog.FileName = stringValue;
+                    }
 
-                    if (openFileDialog.ShowDialog() == DialogResult.OK) value = openFileDialog.FileName;
+                    if (_openFileDialog.ShowDialog() == DialogResult.OK)
+                    {
+                        return _openFileDialog.FileName;
+                    }
                 }
             }
 
@@ -52,24 +48,26 @@ public override object EditValue(ITypeDescriptorContext context, IServiceProvide
         }
 
         /// <summary>>
-        ///         Gets the editing style of the Edit method. If the method
-        ///         is not supported, this will return None.
+        /// Gets the editing style of the Edit method.
         /// </summary>
-        [SuppressMessage("Microsoft.Security", "CA2123:OverrideLinkDemandsShouldBeIdenticalToBase")]
-        // everything in this assembly is full trust.
         public override UITypeEditorEditStyle GetEditStyle(ITypeDescriptorContext context)
         {
             return UITypeEditorEditStyle.Modal;
         }
 
         /// <summary>
-        ///     Initializes the open file dialog when it is created.  This gives you
-        ///     an opportunity to configure the dialog as you please.  The default
-        ///     implementation provides a generic file filter and title.
+        /// Initializes the open file dialog when it is created. This gives you an opportunity to
+        /// configure the dialog as you please. The default implementation provides a generic file
+        /// filter and title.
         /// </summary>
         [SuppressMessage("Microsoft.Design", "CA1011:ConsiderPassingBaseTypesAsParameters")]
         protected virtual void InitializeDialog(OpenFileDialog openFileDialog)
         {
+            if (openFileDialog == null)
+            {
+                throw new ArgumentNullException(nameof(openFileDialog));
+            }
+
             openFileDialog.Filter = SR.GenericFileFilter;
             openFileDialog.Title = SR.GenericOpenFile;
         }
diff --git a/src/System.Windows.Forms.Design.Editors/tests/UnitTests/System/Windows/Forms/Design/FileNameEditorTests.cs b/src/System.Windows.Forms.Design.Editors/tests/UnitTests/System/Windows/Forms/Design/FileNameEditorTests.cs
new file mode 100644
index 00000000000..90a245d1b92
--- /dev/null
+++ b/src/System.Windows.Forms.Design.Editors/tests/UnitTests/System/Windows/Forms/Design/FileNameEditorTests.cs
@@ -0,0 +1,73 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using System.Drawing.Design;
+using System.Windows.Forms;
+using System.Windows.Forms.Design;
+using Moq;
+using Xunit;
+
+namespace System.Windows.Forms.Design.Tests
+{
+    public class FileNameEditorTests
+    {
+        public static IEnumerable<object[]> EditValue_InvalidProvider_TestData()
+        {
+            yield return new object[] { null };
+
+            var nullServiceProviderMock = new Mock<IServiceProvider>(MockBehavior.Strict);
+            nullServiceProviderMock
+                .Setup(p => p.GetService(typeof(IWindowsFormsEditorService)))
+                .Returns(null);
+            yield return new object[] { nullServiceProviderMock.Object };
+
+            var invalidServiceProviderMock = new Mock<IServiceProvider>(MockBehavior.Strict);
+            invalidServiceProviderMock
+                .Setup(p => p.GetService(typeof(IWindowsFormsEditorService)))
+                .Returns(new object());
+            yield return new object[] { invalidServiceProviderMock.Object };
+        }
+
+        [Theory]
+        [MemberData(nameof(EditValue_InvalidProvider_TestData))]
+        public void EditValue_InvalidProvider_ReturnsValue(IServiceProvider provider)
+        {
+            var editor = new FileNameEditor();
+            var value = new object();
+            Assert.Same(value, editor.EditValue(null, provider, value));
+        }
+
+        [Fact]
+        public void GetEditStyle_Invoke_ReturnsModal()
+        {
+            var editor = new FileNameEditor();
+            Assert.Equal(UITypeEditorEditStyle.Modal, editor.GetEditStyle(null));
+        }
+
+        [Fact]
+        public void InitializeDialog_Invoke_Success()
+        {
+            var editor = new SubFileNameEditor();
+            using (var openFileDialog = new OpenFileDialog())
+            {
+                editor.InitializeDialog(openFileDialog);
+                Assert.Equal("All Files(*.*)|*.*", openFileDialog.Filter);
+                Assert.Equal("Open File", openFileDialog.Title);
+            }
+        }
+
+        [Fact]
+        public void InitializeDialog_NullOpenFileDialog_ThrowsArgumentNullException()
+        {
+            var editor = new SubFileNameEditor();
+            Assert.Throws<ArgumentNullException>("openFileDialog", () => editor.InitializeDialog(null));
+        }
+
+        private class SubFileNameEditor : FileNameEditor
+        {
+            public new void InitializeDialog(OpenFileDialog openFileDialog) => base.InitializeDialog(openFileDialog);
+        }
+    }
+}