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Elternbeirat.Web.Tests/PostNeighborsTests.cs

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+using Elternbeirat.Contracts;
+using Elternbeirat.Web.Features.Posts;
+
+namespace Elternbeirat.Web.Tests;
+
+/// <summary>
+/// Unit tests for the older/newer post next to a post. The list comes newest
+/// first, as from PocketBase; "previous" is the older post. Pure logic, no
+/// PocketBase needed.
+/// </summary>
+public class PostNeighborsTests
+{
+    // Newest first, like PocketBaseClient.GetPostsAsync.
+    private static readonly Post[] Posts = [Post("march"), Post("february"), Post("january")];
+
+    private static Post Post(string slug) =>
+        new() { Id = slug, Title = slug, Slug = slug };
+
+    [Fact]
+    public void Middle_post_has_the_older_as_previous_and_the_newer_as_next()
+    {
+        var neighbors = PostNeighbors.Of(Posts, "february");
+
+        neighbors.Previous?.Slug.ShouldBe("january");
+        neighbors.Next?.Slug.ShouldBe("march");
+    }
+
+    [Fact]
+    public void Newest_post_has_no_next()
+    {
+        var neighbors = PostNeighbors.Of(Posts, "march");
+
+        neighbors.Previous?.Slug.ShouldBe("february");
+        neighbors.Next.ShouldBeNull();
+    }
+
+    [Fact]
+    public void Oldest_post_has_no_previous()
+    {
+        var neighbors = PostNeighbors.Of(Posts, "january");
+
+        neighbors.Previous.ShouldBeNull();
+        neighbors.Next?.Slug.ShouldBe("february");
+    }
+
+    [Fact]
+    public void Only_post_has_no_neighbors() =>
+        PostNeighbors.Of([Post("only")], "only").ShouldBe(new PostNeighbors(null, null));
+
+    [Fact]
+    public void Unknown_slug_has_no_neighbors() =>
+        PostNeighbors.Of(Posts, "december").ShouldBe(new PostNeighbors(null, null));
+
+    [Fact]
+    public void Slug_is_compared_case_insensitively() =>
+        PostNeighbors.Of(Posts, "February").Next?.Slug.ShouldBe("march");
+}