test: add unit tests for DocsPageState to verify document management and navigation behavior

Author: Shewart

tests/ShellDocs.Tests/DocsPageStateTests.cs

@@ -0,0 +1,62 @@
+using Microsoft.AspNetCore.Components;
+using ShellDocs.Components;
+using ShellDocs.Core;
+using ShellDocs.Markdown;
+using Xunit;
+
+namespace ShellDocs.Tests;
+
+public class DocsPageStateTests
+{
+    [Fact]
+    public void SetDocument_FiresOnChange_AndStoresDocument()
+    {
+        var (graph, nav) = MinimalGraphAndNav("http://localhost/docs/unknown");
+        var state = new DocsPageState(graph, nav);
+        var doc = new RenderedDocument("<p>hi</p>", Array.Empty<Slot>(), null!, Array.Empty<Heading>());
+
+        var fired = 0;
+        state.OnChange += () => fired++;
+
+        state.SetDocument(doc);
+
+        Assert.Equal(1, fired);
+        Assert.Same(doc, state.Document);
+    }
+
+    [Fact]
+    public void UnknownUrl_YieldsEmptyChromeState()
+    {
+        var (graph, nav) = MinimalGraphAndNav("http://localhost/docs/does-not-exist");
+        var state = new DocsPageState(graph, nav);
+
+        state.SetDocument(null);
+
+        Assert.Null(state.CurrentNode);
+        Assert.Null(state.Prev);
+        Assert.Null(state.Next);
+        Assert.Empty(state.Breadcrumbs);
+    }
+
+    [Fact]
+    public void Dispose_UnsubscribesFromNavigationManager()
+    {
+        var (graph, nav) = MinimalGraphAndNav("http://localhost/");
+        var state = new DocsPageState(graph, nav);
+
+        // Should not throw; sanity that Dispose is idempotent-ish.
+        state.Dispose();
+    }
+
+    private static (NavigationGraph, NavigationManager) MinimalGraphAndNav(string uri)
+    {
+        var root = new NavigationNode { Kind = NodeKind.Section };
+        return (new NavigationGraph(root), new StubNavigationManager(uri));
+    }
+
+    private sealed class StubNavigationManager : NavigationManager
+    {
+        public StubNavigationManager(string uri) => Initialize("http://localhost/", uri);
+        protected override void NavigateToCore(string uri, bool forceLoad) { }
+    }
+}