Add test for health_check endpoint

spec/controllers/health_check_controller_spec.rb

@@ -0,0 +1,13 @@
+require 'rails_helper'
+
+describe HealthCheck::HealthCheckController do
+  render_views
+
+  describe 'GET #show' do
+    subject(:response) { get :index, params: { format: :json } }
+
+    it 'returns the right response' do
+      expect(response).to have_http_status 200
+    end
+  end
+end