Add QrCodesController test

test/controllers/qr_codes_controller_test.rb

@@ -0,0 +1,16 @@
+require "test_helper"
+
+class QrCodesControllerTest < ActionDispatch::IntegrationTest
+  test "show" do
+    join_code = account_join_codes(:"37s")
+    account = accounts("37s")
+    url = join_url(code: join_code.code, script_name: account.slug, host: "app.fizzy.do")
+    signed_token = QrCodeLink.new(url).signed
+
+    get qr_code_path(signed_token)
+
+    assert_response :success
+    assert_match %r{image/svg\+xml}, response.content_type
+    assert_includes response.body, "<svg"
+  end
+end