diff --git a/src/test/unit/System.Windows.Forms/System/Windows/Forms/CheckBoxBaseAdapterTests.cs b/src/test/unit/System.Windows.Forms/System/Windows/Forms/CheckBoxBaseAdapterTests.cs
new file mode 100644
index 00000000000..94cb5ee8710
--- /dev/null
+++ b/src/test/unit/System.Windows.Forms/System/Windows/Forms/CheckBoxBaseAdapterTests.cs
@@ -0,0 +1,301 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Drawing;
+using System.Windows.Forms.ButtonInternal;
+
+namespace System.Windows.Forms.Tests;
+
+public class CheckBoxBaseAdapterTests : IDisposable
+{
+    private TestCheckBox? _checkBox;
+
+    private (TestCheckBoxBaseAdapter, TestCheckBox) CreateAdapter(CheckState checkState)
+    {
+        _checkBox = new TestCheckBox
+        {
+            CheckState = checkState
+        };
+
+        TestCheckBoxBaseAdapter adapter = new(_checkBox);
+
+        return (adapter, _checkBox);
+    }
+
+    public void Dispose() => _checkBox?.Dispose();
+
+    private class TestCheckBox : CheckBox
+    {
+        public new bool Enabled
+        {
+            get => base.Enabled;
+            set => base.Enabled = value;
+        }
+
+        public new CheckState CheckState
+        {
+            get => base.CheckState;
+            set => base.CheckState = value;
+        }
+    }
+
+    private class TestCheckBoxBaseAdapter : CheckBoxBaseAdapter
+    {
+        public TestCheckBoxBaseAdapter(ButtonBase control) : base(control) { }
+
+        public void CallDrawCheckFlat(
+            PaintEventArgs e,
+            LayoutData layout,
+            Color checkColor,
+            Color checkBackground,
+            Color checkBorder,
+            ColorData colors)
+            => DrawCheckFlat(e, layout, checkColor, checkBackground, checkBorder, colors);
+
+        protected override LayoutOptions Layout(PaintEventArgs e)
+            => new LayoutOptions();
+
+        protected override ButtonBaseAdapter CreateButtonAdapter()
+            => new StubButtonBaseAdapter(Control);
+
+        private class StubButtonBaseAdapter : ButtonBaseAdapter
+        {
+            public StubButtonBaseAdapter(ButtonBase control) : base(control) { }
+            internal override void PaintUp(PaintEventArgs e, CheckState state) { }
+            internal override void PaintDown(PaintEventArgs e, CheckState state) { }
+            internal override void PaintOver(PaintEventArgs e, CheckState state) { }
+            protected override LayoutOptions Layout(PaintEventArgs e) => new LayoutOptions();
+        }
+
+        internal override void PaintOver(PaintEventArgs e, CheckState state)
+        {
+        }
+
+        internal override void PaintDown(PaintEventArgs e, CheckState state)
+        {
+        }
+
+        internal override void PaintUp(PaintEventArgs e, CheckState state)
+        {
+        }
+    }
+
+    private static ButtonBaseAdapter.LayoutData CreateLayoutData(bool dotNetOneButtonCompat = false)
+    {
+        ButtonBaseAdapter.LayoutData layout = new(
+            new ButtonBaseAdapter.LayoutOptions
+            {
+                DotNetOneButtonCompat = dotNetOneButtonCompat
+            })
+        {
+            CheckBounds = new Rectangle(2, 2, 11, 11)
+        };
+
+        return layout;
+    }
+
+    private static ButtonBaseAdapter.ColorData CreateColorData(Graphics graphics)
+    {
+        ButtonBaseAdapter.ColorOptions options = new(
+            graphics,
+            Color.Black,
+            Color.White
+        );
+
+        ButtonBaseAdapter.ColorData colorData = new(options)
+        {
+            ButtonFace = Color.LightGray,
+            ButtonShadow = Color.Gray,
+            Highlight = Color.Yellow
+        };
+
+        return colorData;
+    }
+
+    [WinFormsTheory]
+    [InlineData(CheckState.Unchecked, false)]
+    [InlineData(CheckState.Checked, false)]
+    [InlineData(CheckState.Indeterminate, false)]
+    [InlineData(CheckState.Unchecked, true)]
+    [InlineData(CheckState.Checked, true)]
+    [InlineData(CheckState.Indeterminate, true)]
+    public void DrawCheckFlat_DoesNotThrow(CheckState checkState, bool dotNetOneButtonCompat)
+    {
+        (TestCheckBoxBaseAdapter adapter, TestCheckBox checkBox) = CreateAdapter(checkState);
+        using Bitmap bitmap = new(20, 20);
+        using Graphics graphics = Graphics.FromImage(bitmap);
+        using PaintEventArgs e = new(graphics, new Rectangle(0, 0, 20, 20));
+        ButtonBaseAdapter.LayoutData layout = CreateLayoutData(dotNetOneButtonCompat);
+        Color checkColor = Color.Black;
+        Color checkBackground = Color.White;
+        Color checkBorder = Color.Blue;
+        ButtonBaseAdapter.ColorData colors = CreateColorData(graphics);
+
+        Exception? ex = Record.Exception(() =>
+            adapter.CallDrawCheckFlat(e, layout, checkColor, checkBackground, checkBorder, colors));
+
+        ex.Should().BeNull();
+    }
+
+    [WinFormsTheory]
+    [InlineData(false, CheckState.Unchecked, false, 0)]
+    [InlineData(false, CheckState.Unchecked, true, 1)]
+    [InlineData(true, CheckState.Indeterminate, true, 2)]
+    public void DrawCheckBackground_CoversAllBranches(
+        bool controlEnabled,
+        CheckState checkState,
+        bool disabledColors,
+        int expectedBranch)
+    {
+        Rectangle bounds = new(1, 2, 3, 4);
+        using Bitmap bitmap = new(10, 10);
+        using Graphics graphics = Graphics.FromImage(bitmap);
+        Color checkBackground = expectedBranch == 2 ? SystemColors.Window : Color.Red;
+
+        Exception? ex = Record.Exception(() =>
+            CheckBoxBaseAdapter.DrawCheckBackground(
+                controlEnabled,
+                checkState,
+                graphics,
+                bounds,
+                checkBackground,
+                disabledColors));
+
+        ex.Should().BeNull();
+    }
+
+    [WinFormsTheory]
+    [InlineData(CheckState.Checked, true, true)]
+    [InlineData(CheckState.Checked, false, true)]
+    [InlineData(CheckState.Indeterminate, true, true)]
+    [InlineData(CheckState.Indeterminate, false, true)]
+    [InlineData(CheckState.Unchecked, true, false)]
+    public void DrawCheckOnly_Protected_DoesNotThrow(
+        CheckState checkState,
+        bool enabled,
+        bool isChecked)
+    {
+        (TestCheckBoxBaseAdapter adapter, TestCheckBox checkBox) = CreateAdapter(checkState);
+        checkBox.Enabled = enabled;
+        checkBox.Checked = isChecked;
+
+        using Bitmap bitmap = new(20, 20);
+        using Graphics graphics = Graphics.FromImage(bitmap);
+        using PaintEventArgs e = new(graphics, new Rectangle(0, 0, 20, 20));
+        ButtonBaseAdapter.LayoutData layout = CreateLayoutData();
+        ButtonBaseAdapter.ColorData colors = CreateColorData(graphics);
+        Color checkColor = Color.Black;
+
+        Exception? ex = Record.Exception(() =>
+            adapter.TestAccessor().Dynamic.DrawCheckOnly(
+                e,
+                layout,
+                colors,
+                checkColor));
+
+        ex.Should().BeNull();
+    }
+
+    [WinFormsFact]
+    public void DrawPopupBorder_DoesNotThrow_AndInflatesRectangle()
+    {
+        using Bitmap bitmap = new(20, 20);
+        using Graphics graphics = Graphics.FromImage(bitmap);
+        Rectangle original = new(2, 2, 10, 10);
+
+        ButtonBaseAdapter.ColorData colors = CreateColorData(graphics);
+
+        Rectangle result = CheckBoxBaseAdapter.DrawPopupBorder(graphics, original, colors);
+
+        Rectangle expected = original;
+        expected.Inflate(-1, -1);
+
+        result.Should().Be(expected);
+    }
+
+    [WinFormsFact]
+    public void DrawPopupBorder_PaintEventArgs_DoesNotThrow_AndInflatesRectangle()
+    {
+        using Bitmap bitmap = new(20, 20);
+        using Graphics graphics = Graphics.FromImage(bitmap);
+        Rectangle original = new(3, 3, 8, 8);
+
+        ButtonBaseAdapter.ColorData colors = CreateColorData(graphics);
+
+        using PaintEventArgs e = new(graphics, new Rectangle(0, 0, 20, 20));
+        Rectangle result = CheckBoxBaseAdapter.DrawPopupBorder(e, original, colors);
+
+        Rectangle expected = original;
+        expected.Inflate(-1, -1);
+
+        result.Should().Be(expected);
+    }
+
+    [WinFormsFact]
+    public void DrawPopupBorder_HDC_DoesNotThrow_AndInflatesRectangle()
+    {
+        using Bitmap bitmap = new(20, 20);
+        using Graphics graphics = Graphics.FromImage(bitmap);
+        Rectangle original = new(4, 4, 6, 6);
+
+        ButtonBaseAdapter.ColorData colors = CreateColorData(graphics);
+
+        IntPtr hdcPtr = graphics.GetHdc();
+        try
+        {
+            Rectangle result = CheckBoxBaseAdapter.DrawPopupBorder(
+                new HDC(hdcPtr),
+                original,
+                colors);
+
+            Rectangle expected = original;
+            expected.Inflate(-1, -1);
+
+            result.Should().Be(expected);
+        }
+        finally
+        {
+            graphics.ReleaseHdc(hdcPtr);
+        }
+    }
+
+    [Theory]
+    [InlineData(null, true, 2, 2, 10, 10)]
+    [InlineData("", true, 2, 2, 10, 10)]
+    [InlineData(null, false, 2, 2, 10, 10)]
+    [InlineData("", false, 2, 2, 10, 10)]
+    public void AdjustFocusRectangle_SetsFocusAsExpected(
+        string? text,
+        bool autoSize,
+        int checkX, int checkY, int checkW, int checkH)
+    {
+        (TestCheckBoxBaseAdapter adapter, TestCheckBox checkBox) = CreateAdapter(CheckState.Unchecked);
+        checkBox.Text = text;
+        checkBox.AutoSize = autoSize;
+
+        ButtonBaseAdapter.LayoutData layout = new(new ButtonBaseAdapter.LayoutOptions())
+        {
+            CheckBounds = new Rectangle(checkX, checkY, checkW, checkH),
+            Field = new Rectangle(5, 5, 20, 20)
+        };
+
+        adapter.TestAccessor().Dynamic.AdjustFocusRectangle(layout);
+
+        if (string.IsNullOrEmpty(text))
+        {
+            if (autoSize)
+            {
+                Rectangle expected = Rectangle.Inflate(layout.CheckBounds, -2, -2);
+                layout.Focus.Should().Be(expected);
+            }
+            else
+            {
+                layout.Focus.Should().Be(new Rectangle(5, 5, 20, 20));
+            }
+        }
+        else
+        {
+            layout.Focus.Should().Be(default);
+        }
+    }
+}