make blog slug tests content-independent

Commit 1709cb7 deleted the pinned hello-world post and ten tests
silently rotted with it - invisible until now because the suite could
not run in this clone (incomplete deps, then the broken frontmatter).
The slug, banner, og-meta and tag tests now derive slug and title from
the compiled posts at runtime (newest live post, newest draft), matching
the existing latest_post_with_links pattern, so content churn no longer
breaks them.

app/test/firehose_web/controllers/blog_controller_test.exs

@@ -1,6 +1,19 @@
 defmodule FirehoseWeb.BlogControllerTest do
   use FirehoseWeb.ConnCase, async: false
 
+  # Content churns; the behavior under test does not. Pick deterministically
+  # from the compiled posts instead of pinning slugs - the pinned "hello-world"
+  # post was deleted in 1709cb7 and ten tests silently rotted with it.
+  defp a_draft_post do
+    Enum.find(Firehose.EngineeringBlog.all_posts(), &(&1.published == false)) ||
+      raise "no draft (published: false) engineering post to exercise status banners"
+  end
+
+  defp a_live_post do
+    Enum.find(Firehose.EngineeringBlog.all_posts(), &(Blogex.Post.visibility(&1) == :live)) ||
+      raise "no live engineering post to exercise og meta tags"
+  end
+
   describe "GET /blog/:blog_id (index) - date filtering" do
     test "does not show future-dated posts", %{conn: conn} do
       html = conn |> get(~p"/blog/engineering") |> html_response(200)
@@ -26,7 +39,8 @@ defmodule FirehoseWeb.BlogControllerTest do
     setup :register_and_log_in_user
 
     test "authenticated user sees draft banner on draft post", %{conn: conn} do
-      response = conn |> get(~p"/blog/engineering/hello-world")
+      post = a_draft_post()
+      response = conn |> get(~p"/blog/engineering/#{post.id}")
 
       assert html_response(response, 200) =~ "Draft"
       assert response.resp_body =~ "not published"
@@ -49,9 +63,11 @@ defmodule FirehoseWeb.BlogControllerTest do
 
   describe "GET /blog/:blog_id/:slug - no banners for unauthenticated" do
     test "unauthenticated user sees no banner on draft post", %{conn: conn} do
+      post = a_draft_post()
+
       response =
         conn
-        |> get(~p"/blog/engineering/hello-world")
+        |> get(~p"/blog/engineering/#{post.id}")
         |> html_response(200)
 
       refute response =~ "post-status-banner"
@@ -69,26 +85,30 @@ defmodule FirehoseWeb.BlogControllerTest do
 
   describe "GET /blog/:blog_id/:slug - Open Graph meta tags" do
     test "meta tags include og_title", %{conn: conn} do
-      response = conn |> get(~p"/blog/engineering/hello-world") |> html_response(200)
+      post = a_live_post()
+      response = conn |> get(~p"/blog/engineering/#{post.id}") |> html_response(200)
 
       assert response =~ ~s(<meta property="og:title")
-      assert response =~ "Hello World"
+      assert response =~ post.title
     end
 
     test "meta tags include og_description", %{conn: conn} do
-      response = conn |> get(~p"/blog/engineering/hello-world") |> html_response(200)
+      post = a_live_post()
+      response = conn |> get(~p"/blog/engineering/#{post.id}") |> html_response(200)
 
       assert response =~ ~s(<meta property="og:description")
     end
 
     test "meta tags include og_type article", %{conn: conn} do
-      response = conn |> get(~p"/blog/engineering/hello-world") |> html_response(200)
+      post = a_live_post()
+      response = conn |> get(~p"/blog/engineering/#{post.id}") |> html_response(200)
 
       assert response =~ ~s(<meta property="og:type" content="article")
     end
 
     test "meta tags include twitter:card", %{conn: conn} do
-      response = conn |> get(~p"/blog/engineering/hello-world") |> html_response(200)
+      post = a_live_post()
+      response = conn |> get(~p"/blog/engineering/#{post.id}") |> html_response(200)
 
       assert response =~ ~s(<meta name="twitter:card" content="summary_large_image")
     end
@@ -101,10 +121,11 @@ defmodule FirehoseWeb.BlogControllerTest do
     end
 
     test "meta tags have correct og_url", %{conn: conn} do
-      response = conn |> get(~p"/blog/engineering/hello-world") |> html_response(200)
+      post = a_live_post()
+      response = conn |> get(~p"/blog/engineering/#{post.id}") |> html_response(200)
 
       assert response =~
-               ~s(<meta property="og:url" content="http://localhost:4002/blog/engineering/hello-world")
+               ~s(<meta property="og:url" content="http://localhost:4002/blog/engineering/#{post.id}")
     end
   end