Added unit testing

Syrette.Tests/ServiceContainerDisposalTests.cs

@@ -0,0 +1,40 @@
+namespace Syrette.Tests;
+
+public class ServiceContainerDisposalTests
+{
+    [Fact]
+    public void Dispose_disposes_singletons_implementing_IDisposable()
+    {
+        var container = new ServiceContainer();
+        container.AddSingleton<TestDisposableService>();
+        var instance = container.GetService<TestDisposableService>();
+
+        container.Dispose();
+        Assert.True(instance.IsDisposed);
+    }
+
+    [Fact]
+    public void Dispose_clears_singleton_cache()
+    {
+        var container = new ServiceContainer();
+        container.AddSingleton<TestDisposableService>();
+        container.GetService<TestDisposableService>();
+
+        container.Dispose();
+
+        Assert.Throws<InvalidOperationException>(() =>
+            container.GetService<TestDisposableService>());
+    }
+
+    [Fact]
+    public void Multiple_dispose_is_safe()
+    {
+        var container = new ServiceContainer();
+        container.AddSingleton<TestDisposableService>();
+        container.GetService<TestDisposableService>();
+
+        container.Dispose();
+        container.Dispose();
+        Assert.True(true);
+    }
+}