test(msdf): add tests for MsdfSpriteText presence behavior

tests/Sprites/TestSceneMsdfSpriteTextPresence.cs

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+using kajarlabs.osu.Framework.MsdfTextRendering.Graphics.Sprites;
+using kajarlabs.osu.Framework.MsdfTextRendering.Tests.Visual;
+using NUnit.Framework;
+using osu.Framework.Extensions.Color4Extensions;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Graphics.Shapes;
+using osu.Framework.Graphics.Sprites;
+using osu.Framework.Testing;
+using osu.Framework.Utils;
+using osuTK.Graphics;
+
+namespace kajarlabs.osu.Framework.MsdfTextRendering.Tests.Sprites;
+
+[HeadlessTest]
+public partial class TestSceneMsdfSpriteTextPresence : SampleTestScene
+{
+    [Test]
+    public void TestNormalSpriteText()
+    {
+        Container container = null!;
+        MsdfSpriteText text = null!;
+
+        AddStep("reset", () =>
+        {
+            Child = container = new Container
+            {
+                Anchor = Anchor.Centre,
+                Origin = Anchor.Centre,
+                AutoSizeAxes = Axes.Both,
+                Children =
+                [
+                        new Box
+                        {
+                            RelativeSizeAxes = Axes.Both,
+                            Colour = Color4.Red.Opacity(0.3f)
+                        },
+                        text = new MsdfSpriteText
+                        {
+                            Text = "Hello world!",
+                            Font = new FontUsage("WorkSans", 12, "Regular"),
+                        }
+                ]
+            };
+        });
+
+        AddAssert("is present", () => text.IsPresent);
+        AddAssert("height == 12", () => Precision.AlmostEquals(12, container.Height));
+        AddStep("empty text", () => text.Text = string.Empty);
+        AddAssert("not present", () => !text.IsPresent);
+        AddAssert("height == 0", () => Precision.AlmostEquals(0, container.Height));
+    }
+
+    [Test]
+    public void TestAlwaysPresentSpriteText()
+    {
+        Container container = null!;
+        MsdfSpriteText text = null!;
+
+        AddStep("reset", () =>
+        {
+            Child = container = new Container
+            {
+                Anchor = Anchor.Centre,
+                Origin = Anchor.Centre,
+                AutoSizeAxes = Axes.Both,
+                Children =
+                [
+                        new Box
+                        {
+                            RelativeSizeAxes = Axes.Both,
+                            Colour = Color4.Red.Opacity(0.3f)
+                        },
+                        text = new AlwaysPresentSpriteText
+                        {
+                            Text = "Hello world!",
+                            Font = new FontUsage(size: 12),
+                        }
+                ]
+            };
+        });
+
+        AddAssert("is present", () => text.IsPresent);
+        AddAssert("height == 12", () => Precision.AlmostEquals(12, container.Height));
+        AddStep("empty text", () => text.Text = string.Empty);
+        AddAssert("is present", () => text.IsPresent);
+        AddAssert("height == 0", () => Precision.AlmostEquals(0, container.Height));
+    }
+
+    [Test]
+    public void TestPresenceRemainsTheSameDuringFlow()
+    {
+        AddStep("reset", () =>
+        {
+            Child = new FillFlowContainer
+            {
+                Child = new MsdfSpriteText()
+            };
+        });
+
+        AddWaitStep("wait for some update frames", 2);
+    }
+
+    private partial class AlwaysPresentSpriteText : MsdfSpriteText
+    {
+        public override bool IsPresent => true;
+    }
+}