From https://once.com/writebook

test/controllers/join_codes_controller_test.rb

@@ -0,0 +1,20 @@
+require "test_helper"
+
+class Accounts::JoinCodesControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    sign_in :david
+  end
+
+  test "create new join code" do
+    assert_changes -> { accounts(:signal).reload.join_code } do
+      post account_join_code_url
+      assert_redirected_to users_url
+    end
+  end
+
+  test "only administrators can create new join codes" do
+    sign_in :jz
+    post account_join_code_url
+    assert_response :forbidden
+  end
+end