From https://once.com/writebook

test/controllers/sessions/transfers-controller_test.rb

@@ -0,0 +1,18 @@
+require "test_helper"
+
+class Sessions::TransfersControllerTest < ActionDispatch::IntegrationTest
+  test "show renders when not signed in" do
+    get session_transfer_url("some-token")
+
+    assert_response :success
+  end
+
+  test "update establishes a session when the code is valid" do
+    user = users(:david)
+
+    put session_transfer_url(user.transfer_id)
+
+    assert_redirected_to root_url
+    assert parsed_cookies.signed[:session_token]
+  end
+end