Add some tests for KeyboardDevice.

Including failing tests for #3127.

tests/Avalonia.Input.UnitTests/KeyboardDeviceTests.cs

@@ -0,0 +1,90 @@
+using Avalonia.Input.Raw;
+using Avalonia.Interactivity;
+using Moq;
+using Xunit;
+
+namespace Avalonia.Input.UnitTests
+{
+    public class KeyboardDeviceTests
+    {
+        [Fact]
+        public void Keypresses_Should_Be_Sent_To_Root_If_No_Focused_Element()
+        {
+            var target = new KeyboardDevice();
+            var root = new Mock<IInputRoot>();
+
+            target.ProcessRawEvent(
+                new RawKeyEventArgs(
+                    target,
+                    0,
+                    root.Object,
+                    RawKeyEventType.KeyDown,
+                    Key.A,
+                    RawInputModifiers.None));
+
+            root.Verify(x => x.RaiseEvent(It.IsAny<KeyEventArgs>()));
+        }
+
+        [Fact]
+        public void Keypresses_Should_Be_Sent_To_Focused_Element()
+        {
+            var target = new KeyboardDevice();
+            var focused = new Mock<IInputElement>();
+            var root = Mock.Of<IInputRoot>();
+
+            target.SetFocusedElement(
+                focused.Object,
+                NavigationMethod.Unspecified,
+                InputModifiers.None);
+
+            target.ProcessRawEvent(
+                new RawKeyEventArgs(
+                    target,
+                    0,
+                    root,
+                    RawKeyEventType.KeyDown,
+                    Key.A,
+                    RawInputModifiers.None));
+
+            focused.Verify(x => x.RaiseEvent(It.IsAny<KeyEventArgs>()));
+        }
+
+        [Fact]
+        public void TextInput_Should_Be_Sent_To_Root_If_No_Focused_Element()
+        {
+            var target = new KeyboardDevice();
+            var root = new Mock<IInputRoot>();
+
+            target.ProcessRawEvent(
+                new RawTextInputEventArgs(
+                    target,
+                    0,
+                    root.Object,
+                    "Foo"));
+
+            root.Verify(x => x.RaiseEvent(It.IsAny<TextInputEventArgs>()));
+        }
+
+        [Fact]
+        public void TextInput_Should_Be_Sent_To_Focused_Element()
+        {
+            var target = new KeyboardDevice();
+            var focused = new Mock<IInputElement>();
+            var root = Mock.Of<IInputRoot>();
+
+            target.SetFocusedElement(
+                focused.Object,
+                NavigationMethod.Unspecified,
+                InputModifiers.None);
+
+            target.ProcessRawEvent(
+                new RawTextInputEventArgs(
+                    target,
+                    0,
+                    root,
+                    "Foo"));
+
+            focused.Verify(x => x.RaiseEvent(It.IsAny<TextInputEventArgs>()));
+        }
+    }
+}