fix: self-follow validation + add follow/unfollow tests

Self-follow check used get_attribute(:follower_id) which is nil at
validation time because relate_actor runs after validations in Ash.
Fixed to use context.actor.id directly.

Added 9 tests covering: follow, follow idempotency, self-follow
prevention, guest restriction, unfollow, unfollow noop,
guest unfollow, follower/following counts, and am_i_following.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fix_plan.md

@@ -11,11 +11,13 @@
 
 ## Backlog
 
+- [x] Self-follow validation used `get_attribute(:follower_id)` which is nil at validation time (relate_actor runs after) — fixed to use `context.actor.id`
+- [x] Follow/unfollow test coverage (9 tests)
 - [ ] No pagination on user list (`/users`)
 - [ ] No CHECK constraint on `likes >= 0` at DB level (low priority, app logic prevents it)
-- [ ] `read :following_feed` returns error if actor is nil — should be policy-guarded
+- [ ] `read :following_feed` — nil actor returns empty list (not a bug)
 - [ ] No search for users or tweets
-- [ ] Missing test coverage: follow/unfollow, comments, tweet creation, auth flows
+- [ ] Missing test coverage: comments, tweet creation, auth flows
 
 ## Notes
 

lib/mixer/accounts/follow.ex

@@ -31,11 +31,11 @@ defmodule Mixer.Accounts.Follow do
       accept [:following_id]
       change relate_actor(:follower)
 
-      validate fn changeset, _context ->
-        follower_id = Ash.Changeset.get_attribute(changeset, :follower_id)
+      validate fn changeset, context ->
+        actor_id = context.actor && context.actor.id
         following_id = Ash.Changeset.get_attribute(changeset, :following_id)
 
-        if follower_id == following_id do
+        if actor_id && actor_id == following_id do
           {:error, field: :following_id, message: "You cannot follow yourself"}
         else
           :ok

test/mixer/accounts/follow_test.exs

@@ -0,0 +1,172 @@
+defmodule Mixer.Accounts.FollowTest do
+  use Mixer.DataCase, async: true
+
+  require Ash.Query
+
+  alias Mixer.Accounts.Follow
+  alias Mixer.Accounts.User
+
+  describe "follow" do
+    test "a user can follow another user" do
+      alice = user_fixture("alice@example.com", "alice")
+      bob = user_fixture("bob@example.com", "bob")
+
+      assert {:ok, follow} =
+               Follow
+               |> Ash.Changeset.for_create(:follow, %{following_id: bob.id}, actor: alice)
+               |> Ash.create()
+
+      assert follow.follower_id == alice.id
+      assert follow.following_id == bob.id
+    end
+
+    test "following the same user twice is a noop (upsert)" do
+      alice = user_fixture("alice2@example.com", "alice2")
+      bob = user_fixture("bob2@example.com", "bob2")
+
+      assert {:ok, _} =
+               Follow
+               |> Ash.Changeset.for_create(:follow, %{following_id: bob.id}, actor: alice)
+               |> Ash.create()
+
+      assert {:ok, _} =
+               Follow
+               |> Ash.Changeset.for_create(:follow, %{following_id: bob.id}, actor: alice)
+               |> Ash.create()
+
+      assert count_follows(alice.id, bob.id) == 1
+    end
+
+    test "a user cannot follow themselves" do
+      alice = user_fixture("alice3@example.com", "alice3")
+
+      assert {:error, error} =
+               Follow
+               |> Ash.Changeset.for_create(:follow, %{following_id: alice.id}, actor: alice)
+               |> Ash.create()
+
+      assert Exception.message(error) =~ "cannot follow yourself"
+    end
+
+    test "guests cannot follow" do
+      bob = user_fixture("bob3@example.com", "bob3")
+
+      assert {:error, _error} =
+               Follow
+               |> Ash.Changeset.for_create(:follow, %{following_id: bob.id})
+               |> Ash.create()
+    end
+  end
+
+  describe "unfollow" do
+    test "a user can unfollow someone they follow" do
+      alice = user_fixture("alice4@example.com", "alice4")
+      bob = user_fixture("bob4@example.com", "bob4")
+
+      Follow
+      |> Ash.Changeset.for_create(:follow, %{following_id: bob.id}, actor: alice)
+      |> Ash.create!()
+
+      assert count_follows(alice.id, bob.id) == 1
+
+      assert :ok =
+               Follow
+               |> Ash.ActionInput.for_action(:unfollow, %{following_id: bob.id}, actor: alice)
+               |> Ash.run_action()
+
+      assert count_follows(alice.id, bob.id) == 0
+    end
+
+    test "unfollowing when not following is a noop" do
+      alice = user_fixture("alice5@example.com", "alice5")
+      bob = user_fixture("bob5@example.com", "bob5")
+
+      assert :ok =
+               Follow
+               |> Ash.ActionInput.for_action(:unfollow, %{following_id: bob.id}, actor: alice)
+               |> Ash.run_action()
+
+      assert count_follows(alice.id, bob.id) == 0
+    end
+
+    test "guests cannot unfollow" do
+      bob = user_fixture("bob6@example.com", "bob6")
+
+      assert {:error, error} =
+               Follow
+               |> Ash.ActionInput.for_action(:unfollow, %{following_id: bob.id})
+               |> Ash.run_action()
+
+      assert Exception.message(error) =~ "forbidden"
+    end
+  end
+
+  describe "follower/following counts" do
+    test "follower_count and following_count reflect current follows" do
+      alice = user_fixture("alice6@example.com", "alice6")
+      bob = user_fixture("bob7@example.com", "bob7")
+      carol = user_fixture("carol@example.com", "carol")
+
+      Follow
+      |> Ash.Changeset.for_create(:follow, %{following_id: bob.id}, actor: alice)
+      |> Ash.create!()
+
+      Follow
+      |> Ash.Changeset.for_create(:follow, %{following_id: carol.id}, actor: alice)
+      |> Ash.create!()
+
+      Follow
+      |> Ash.Changeset.for_create(:follow, %{following_id: bob.id}, actor: carol)
+      |> Ash.create!()
+
+      alice_loaded = User |> Ash.get!(alice.id, load: [:follower_count, :following_count], authorize?: false)
+      bob_loaded = User |> Ash.get!(bob.id, load: [:follower_count, :following_count], authorize?: false)
+
+      assert alice_loaded.following_count == 2
+      assert alice_loaded.follower_count == 0
+      assert bob_loaded.follower_count == 2
+      assert bob_loaded.following_count == 0
+    end
+
+    test "am_i_following reflects the actor's follow status" do
+      alice = user_fixture("alice7@example.com", "alice7")
+      bob = user_fixture("bob8@example.com", "bob8")
+
+      not_following =
+        User |> Ash.get!(bob.id, actor: alice, load: [:am_i_following], authorize?: false)
+
+      refute not_following.am_i_following
+
+      Follow
+      |> Ash.Changeset.for_create(:follow, %{following_id: bob.id}, actor: alice)
+      |> Ash.create!()
+
+      following =
+        User |> Ash.get!(bob.id, actor: alice, load: [:am_i_following], authorize?: false)
+
+      assert following.am_i_following
+    end
+  end
+
+  # ── fixtures ──────────────────────────────────────────────────────────────
+
+  defp user_fixture(email, username) do
+    User
+    |> Ash.Changeset.for_create(:register_with_password, %{
+      email: email,
+      password: "password1234",
+      password_confirmation: "password1234",
+      username: username
+    })
+    |> Ash.create!(authorize?: false)
+  end
+
+  defp count_follows(follower_id, following_id) do
+    Follow
+    |> Ash.Query.filter(
+      Ash.Expr.expr(follower_id == ^follower_id and following_id == ^following_id)
+    )
+    |> Ash.read!(authorize?: false)
+    |> length()
+  end
+end