Add /api/v1_alpha/accounts/:id/in_collections to list collections you are in (#38657)

spec/requests/api/v1_alpha/in_collections_spec.rb

@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'Api::V1Alpha::InCollections', feature: :collections do
+  include_context 'with API authentication', oauth_scopes: 'read:collections write:collections'
+
+  describe 'GET /api/v1_alpha/in_collections' do
+    subject do
+      get "/api/v1_alpha/accounts/#{account.id}/in_collections", headers: headers, params: params
+    end
+
+    let(:params) { {} }
+    let(:account) { user.account }
+
+    before { Fabricate.times(3, :collection_item, account: account) }
+
+    it 'returns all collections for the given account and http success' do
+      subject
+
+      expect(response).to have_http_status(200)
+      expect(response.parsed_body[:collections].size).to eq 3
+    end
+
+    context 'with limit param' do
+      let(:params) { { limit: '1' } }
+
+      it 'returns only a single result' do
+        subject
+
+        expect(response).to have_http_status(200)
+        expect(response.parsed_body[:collections].size).to eq 1
+
+        expect(response)
+          .to include_pagination_headers(
+            next: api_v1_alpha_account_in_collections_url(account, limit: 1, offset: 1)
+          )
+      end
+    end
+
+    context 'with limit and offset params' do
+      let(:params) { { limit: '1', offset: '1' } }
+
+      it 'returns the correct result and headers' do
+        subject
+
+        expect(response).to have_http_status(200)
+        expect(response.parsed_body[:collections].size).to eq 1
+
+        expect(response)
+          .to include_pagination_headers(
+            prev: api_v1_alpha_account_in_collections_url(account, limit: 1, offset: 0),
+            next: api_v1_alpha_account_in_collections_url(account, limit: 1, offset: 2)
+          )
+      end
+    end
+
+    context 'when requested account is different from current account' do
+      let(:account) { Fabricate(:account) }
+
+      it 'returns http forbidden' do
+        subject
+
+        expect(response)
+          .to have_http_status(403)
+      end
+    end
+  end
+end