Implement ping/pong endpoint in API

spec/integration/api/application_spec.rb

@@ -0,0 +1,13 @@
+describe 'API application' do
+  include AcceptanceHelpers
+
+  before { api_sign_in }
+
+  describe 'ping endpoint' do
+    before { get api_ping_path, format: json }
+
+    it 'responds with a pong' do
+      expect(json).to eq({ pong: 'ok' })
+    end
+  end
+end