fix and test

src/Avalonia.Controls/TextBox.cs

@@ -287,8 +287,6 @@ namespace Avalonia.Controls
             {
                 DecideCaretVisibility();
             }
-
-            e.Handled = true;
         }
 
         private void DecideCaretVisibility()

tests/Avalonia.Controls.UnitTests/TextBoxTests.cs

@@ -401,6 +401,53 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void TextBox_GotFocus_And_LostFocus_Work_Properly()
+        {
+            using (UnitTestApplication.Start(FocusServices))
+            {
+                var target1 = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    Text = "1234"
+                };
+                var target2 = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    Text = "5678"
+                };
+                var sp = new StackPanel();
+                sp.Children.Add(target1);
+                sp.Children.Add(target2);
+
+                var root = new TestRoot { Child = sp };
+
+                var gfcount = 0;
+                var lfcount = 0;
+
+                target1.GotFocus += (s, e) => gfcount++;
+                target2.LostFocus += (s, e) => lfcount++;
+
+                target2.Focus();
+                Assert.False(target1.IsFocused);
+                Assert.True(target2.IsFocused);
+
+                target1.Focus();
+                Assert.False(target2.IsFocused);
+                Assert.True(target1.IsFocused);
+
+                Assert.Equal(1, gfcount);
+                Assert.Equal(1, lfcount);
+            }
+        }
+
+        private static TestServices FocusServices => TestServices.MockThreadingInterface.With(
+            focusManager: new FocusManager(),
+            keyboardDevice: () => new KeyboardDevice(),
+            keyboardNavigation: new KeyboardNavigationHandler(),
+            inputManager: new InputManager(),
+            standardCursorFactory: Mock.Of<IStandardCursorFactory>());
+
         private static TestServices Services => TestServices.MockThreadingInterface.With(
             standardCursorFactory: Mock.Of<IStandardCursorFactory>());