Improve api/v1/markers#create performance against simultaneous requests (#28718)

spec/requests/api/v1/markers_spec.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'API Markers' do
+  let(:user)    { Fabricate(:user) }
+  let(:scopes)  { 'read:statuses write:statuses' }
+  let(:token)   { Fabricate(:accessible_access_token, resource_owner_id: user.id, scopes: scopes) }
+  let(:headers) { { 'Authorization' => "Bearer #{token.token}" } }
+
+  describe 'GET /api/v1/markers' do
+    before do
+      Fabricate(:marker, timeline: 'home', last_read_id: 123, user: user)
+      Fabricate(:marker, timeline: 'notifications', last_read_id: 456, user: user)
+
+      get '/api/v1/markers', headers: headers, params: { timeline: %w(home notifications) }
+    end
+
+    it 'returns markers', :aggregate_failures do
+      json = body_as_json
+
+      expect(response).to have_http_status(200)
+      expect(json.key?(:home)).to be true
+      expect(json[:home][:last_read_id]).to eq '123'
+      expect(json.key?(:notifications)).to be true
+      expect(json[:notifications][:last_read_id]).to eq '456'
+    end
+  end
+
+  describe 'POST /api/v1/markers' do
+    context 'when no marker exists' do
+      before do
+        post '/api/v1/markers', headers: headers, params: { home: { last_read_id: '69420' } }
+      end
+
+      it 'creates a marker', :aggregate_failures do
+        expect(response).to have_http_status(200)
+        expect(user.markers.first.timeline).to eq 'home'
+        expect(user.markers.first.last_read_id).to eq 69_420
+      end
+    end
+
+    context 'when a marker exists' do
+      before do
+        post '/api/v1/markers', headers: headers, params: { home: { last_read_id: '69420' } }
+        post '/api/v1/markers', headers: headers, params: { home: { last_read_id: '70120' } }
+      end
+
+      it 'updates a marker', :aggregate_failures do
+        expect(response).to have_http_status(200)
+        expect(user.markers.first.timeline).to eq 'home'
+        expect(user.markers.first.last_read_id).to eq 70_120
+      end
+    end
+  end
+end