Add spec for Api::V1::Instances::ActivityController (#9545)

spec/controllers/api/v1/instances/activity_controller_spec.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Api::V1::Instances::ActivityController, type: :controller do
+  describe 'GET #show' do
+    it 'returns 200' do
+      get :show
+      expect(response).to have_http_status(200)
+    end
+
+    context '!Setting.activity_api_enabled' do
+      it 'returns 404' do
+        Setting.activity_api_enabled = false
+
+        get :show
+        expect(response).to have_http_status(404)
+      end
+    end
+  end
+end