Create a test for Home timeline query missing index

test/pleroma/web/activity_pub/activity_pub_query_test.exs

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+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.ActivityPubQueryTest do
+  use Pleroma.DataCase
+  use Oban.Testing, repo: Pleroma.Repo
+
+  alias Pleroma.Repo
+  alias Pleroma.User
+  alias Pleroma.Web.ActivityPub.ActivityPub
+
+  import Pleroma.Factory
+
+  test "fetch_activities_query/2 indexes" do
+    # Add a few accounts for good measure
+    insert_list(3, :user)
+
+    user = insert(:user)
+    follower = insert(:user)
+
+    # Create a follower
+    User.follow(follower, user)
+
+    # Same opts used by the Home timeline
+    opts = %{
+      type: ["Create", "Announce"],
+      blocking_user: user,
+      muting_user: user,
+      reply_filtering_user: user,
+      announce_filtering_user: user,
+      user: user
+    }
+
+    # I don't fully understand this but it's what the Home timeline does
+    recipients = [user.ap_id | User.following(user)]
+
+    # Build the query
+    query = ActivityPub.fetch_activities_query(recipients, opts)
+
+    # Performs an EXPLAIN, fail if it's a sequence scan
+    refute Repo.explain(:all, query) =~ "Seq Scan"
+  end
+end