Add test coverage

osu.Game.Tests/Visual/UserInterface/TestSceneSearchTextBox.cs

@@ -0,0 +1,38 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using NUnit.Framework;
+using osu.Framework.Graphics;
+using osu.Game.Graphics.UserInterface;
+using osuTK;
+
+namespace osu.Game.Tests.Visual.UserInterface
+{
+    public partial class TestSceneSearchTextBox : OsuTestScene
+    {
+        private SearchTextBox textBox = null!;
+
+        [SetUp]
+        public void SetUp() => Schedule(() =>
+        {
+            Child = textBox = new SearchTextBox
+            {
+                Anchor = Anchor.Centre,
+                Origin = Anchor.Centre,
+                Width = 400,
+                Scale = new Vector2(2f),
+                HoldFocus = true,
+            };
+        });
+
+        [Test]
+        public void TestSelectionOnFocus()
+        {
+            AddStep("set text", () => textBox.Text = "some text");
+            AddAssert("no text selected", () => textBox.SelectedText == string.Empty);
+            AddStep("hide text box", () => textBox.Hide());
+            AddStep("show text box", () => textBox.Show());
+            AddAssert("search text selected", () => textBox.SelectedText == textBox.Text);
+        }
+    }
+}