Deduplicate IDs in relationships and familiar_followers APIs (#27982)

spec/controllers/api/v1/accounts/familiar_followers_controller_spec.rb

@@ -19,5 +19,17 @@ describe Api::V1::Accounts::FamiliarFollowersController do
 
       expect(response).to have_http_status(200)
     end
+
+    context 'when there are duplicate account IDs in the params' do
+      let(:account_a) { Fabricate(:account) }
+      let(:account_b) { Fabricate(:account) }
+
+      it 'removes duplicate account IDs from params' do
+        account_ids = [account_a, account_b, account_b, account_a, account_a].map { |a| a.id.to_s }
+        get :index, params: { id: account_ids }
+
+        expect(body_as_json.pluck(:id)).to eq [account_a.id.to_s, account_b.id.to_s]
+      end
+    end
   end
 end