Add coverage for `AccountPin` model (#33231)

app/models/account_pin.rb

@@ -23,6 +23,6 @@ class AccountPin < ApplicationRecord
   private
 
   def validate_follow_relationship
-    errors.add(:base, I18n.t('accounts.pin_errors.following')) unless account.following?(target_account)
+    errors.add(:base, I18n.t('accounts.pin_errors.following')) unless account&.following?(target_account)
   end
 end

spec/models/account_pin_spec.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe AccountPin do
+  describe 'Associations' do
+    it { is_expected.to belong_to(:account).required }
+    it { is_expected.to belong_to(:target_account).required }
+  end
+
+  describe 'Validations' do
+    describe 'the follow relationship' do
+      subject { Fabricate.build :account_pin, account: account }
+
+      let(:account) { Fabricate :account }
+      let(:target_account) { Fabricate :account }
+
+      context 'when account is following target account' do
+        before { account.follow!(target_account) }
+
+        it { is_expected.to allow_value(target_account).for(:target_account).against(:base) }
+      end
+
+      context 'when account is not following target account' do
+        it { is_expected.to_not allow_value(target_account).for(:target_account).against(:base).with_message(not_following_message) }
+
+        def not_following_message
+          I18n.t('accounts.pin_errors.following')
+        end
+      end
+    end
+  end
+end