Add coverage for `AccountAlias` validations (#31936)

spec/models/account_alias_spec.rb

@@ -8,4 +8,26 @@ RSpec.describe AccountAlias do
       it { is_expected.to normalize(:acct).from('  @username@domain  ').to('username@domain') }
     end
   end
+
+  describe 'Validations' do
+    subject { described_class.new(account:) }
+
+    let(:account) { Fabricate :account }
+
+    it { is_expected.to_not allow_values(nil, '').for(:uri).against(:acct).with_message(not_found_message) }
+
+    it { is_expected.to_not allow_values(account_uri).for(:uri).against(:acct).with_message(self_move_message) }
+
+    def account_uri
+      ActivityPub::TagManager.instance.uri_for(subject.account)
+    end
+
+    def not_found_message
+      I18n.t('migrations.errors.not_found')
+    end
+
+    def self_move_message
+      I18n.t('migrations.errors.move_to_self')
+    end
+  end
 end