tests: add test that validates the metadata of all posts

test/Blog.Tests/Unit/PostMetadataTests.cs

@@ -0,0 +1,95 @@
+using System.Text.Json;
+
+using Markdig;
+using Markdig.Syntax;
+
+namespace Blog.Tests.Unit;
+
+[TestFixture]
+public class PostMetadataTests
+{
+  private static readonly MarkdownPipeline MarkdownPipeline = new MarkdownPipelineBuilder()
+    .UseAdvancedExtensions()
+    .Build();
+
+  private static readonly JsonSerializerOptions JsonSerializerOptions = new()
+  {
+    PropertyNameCaseInsensitive = true,
+    AllowTrailingCommas = true,
+  };
+
+  private const string MetaFence = "meta";
+
+
+  [Test]
+  public void PostsDirectory_ShouldContainIndexFiles()
+  {
+    var postsDir = GetPostsDirectory();
+    var files = Directory.GetFiles(postsDir, "index.md", SearchOption.AllDirectories);
+
+    files.Should().NotBeEmpty("The wwwroot/posts directory should contain blog posts with index.md files.");
+  }
+
+  [TestCaseSource(nameof(GetPostIndexFiles))]
+  public async Task IndexMd_Metadata_CanBeProperlyParsedAndRead(string filePath)
+  {
+    var markdown = await File.ReadAllTextAsync(filePath);
+    var document = Markdown.Parse(markdown, MarkdownPipeline);
+
+    var metadataBlock = document
+      .OfType<FencedCodeBlock>()
+      .FirstOrDefault(block =>
+        block.Arguments is not null &&
+        block.Arguments.Contains(MetaFence)
+      );
+
+    metadataBlock.Should().NotBeNull($"file '{filePath}' should contain a fenced code block with '{MetaFence}' argument.");
+
+    var jsonContent = metadataBlock.Lines.ToString();
+
+    jsonContent.Should().NotBeNullOrWhiteSpace($"metadata code block in '{filePath}' should not be empty.");
+
+    Post? post = null;
+
+    Action deserializeAction = () => post = JsonSerializer.Deserialize<Post>(jsonContent, JsonSerializerOptions);
+
+    deserializeAction.Should().NotThrow($"JSON metadata in '{filePath}' should be valid JSON matching the Post record schema.");
+
+    post.Should().NotBeNull($"deserialized Post from '{filePath}' should not be null.");
+    post.Title.Should().NotBeNullOrWhiteSpace($"post in '{filePath}' must have a title.");
+    post.Lead.Should().NotBeNullOrWhiteSpace($"post in '{filePath}' must have a lead summary.");
+    post.PublishedAt.Should().NotBe(default, $"post in '{filePath}' must have a valid published date.");
+    post.OpenGraphImage.Should().NotBeNullOrWhiteSpace($"post in '{filePath}' must have an openGraphImage path.");
+  }
+
+  private static string GetPostsDirectory()
+  {
+    var current = new DirectoryInfo(AppContext.BaseDirectory);
+
+    while (current is not null)
+    {
+      var candidate = Path.Combine(current.FullName, "src", "Blog", "wwwroot", "posts");
+
+      if (Directory.Exists(candidate))
+      {
+        return candidate;
+      }
+
+      current = current.Parent;
+    }
+
+    throw new DirectoryNotFoundException($"Could not locate 'src/Blog/wwwroot/posts' starting from '{AppContext.BaseDirectory}'.");
+  }
+
+  private static IEnumerable<TestCaseData> GetPostIndexFiles()
+  {
+    var postsDir = GetPostsDirectory();
+    var files = Directory.GetFiles(postsDir, "index.md", SearchOption.AllDirectories);
+
+    foreach (var file in files)
+    {
+      var relativePath = Path.GetRelativePath(postsDir, file);
+      yield return new TestCaseData(file).SetName($"PostMetadata_{relativePath.Replace('\\', '/')}");
+    }
+  }
+}