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
 

app/test/firehose_web/controllers/blog_tags_test.exs

@@ -1,12 +1,25 @@
 defmodule FirehoseWeb.BlogTagsTest do
   use FirehoseWeb.ConnCase
 
+  # Content churns; the behavior under test does not. The newest live post
+  # with a tag is a deterministic stand-in, and tag pages sort date-descending,
+  # so it is on page 1 whatever else is published under that tag. (The pinned
+  # "Hello World" post was deleted in 1709cb7 and this test silently rotted.)
+  defp a_newest_live_post_with_tag do
+    Enum.find(Firehose.EngineeringBlog.all_posts(), fn post ->
+      Blogex.Post.visibility(post) == :live and post.tags != []
+    end) || raise "no live tagged engineering post to exercise the tag page"
+  end
+
   describe "engineering blog tags" do
     test "GET /blog/engineering/tag/:tag shows tag page with filtered posts", %{conn: conn} do
-      body = conn |> get("/blog/engineering/tag/elixir") |> html_response(200)
-      assert body =~ ~s(tagged "elixir")
+      post = a_newest_live_post_with_tag()
+      tag = hd(post.tags)
+
+      body = conn |> get("/blog/engineering/tag/#{tag}") |> html_response(200)
+      assert body =~ ~s(tagged "#{tag}")
       assert body =~ "Engineering Blog"
-      assert body =~ "Hello World"
+      assert body =~ post.title
     end
 
     test "GET /blog/engineering/tag/:tag shows empty list for nonexistent tag", %{conn: conn} do

app/test/firehose_web/controllers/blog_test.exs

@@ -9,6 +9,14 @@ defmodule FirehoseWeb.BlogTest do
     body
   end
 
+  # Content churns; the behavior under test does not. The newest live post is
+  # a deterministic stand-in - the pinned "hello-world" post was deleted in
+  # 1709cb7 and the slug tests silently rotted with it.
+  defp a_live_post do
+    Enum.find(Firehose.EngineeringBlog.all_posts(), &(Blogex.Post.visibility(&1) == :live)) ||
+      raise "no live engineering post to exercise the post pages"
+  end
+
   describe "engineering blog (HTML)" do
     test "GET /blog/engineering returns HTML index with layout", %{conn: conn} do
       body = visit_blog_page(conn, "engineering")
@@ -17,8 +25,9 @@ defmodule FirehoseWeb.BlogTest do
     end
 
     test "GET /blog/engineering/:slug returns HTML post with layout", %{conn: conn} do
-      body = visit_blog_page(conn, "engineering", "/hello-world")
-      assert body =~ "Hello World"
+      post = a_live_post()
+      body = visit_blog_page(conn, "engineering", "/#{post.id}")
+      assert body =~ post.title
     end
 
     test "GET /blog/engineering?page=2 shows the next page of older posts", %{conn: conn} do
@@ -191,11 +200,16 @@ defmodule FirehoseWeb.BlogTest do
     end
 
     test "GET /api/blog/engineering/:slug returns a post", %{conn: conn} do
-      assert %{"id" => "hello-world", "title" => "Hello World"} =
+      post = a_live_post()
+
+      assert %{"id" => id, "title" => title} =
                conn
                |> put_req_header("accept", "application/json")
-               |> get("/api/blog/engineering/hello-world")
+               |> get("/api/blog/engineering/#{post.id}")
                |> json_response(200)
+
+      assert id == post.id
+      assert title == post.title
     end
 
     test "GET /api/blog/engineering/:slug returns 404 for missing post", %{conn: conn} do