e;

    const file = new File([], "filename");
    const dataTransfer = new DataTransfer();
    dataTransfer.items.add(file);
    form.querySelector('input[name=file]').files = dataTransfer.files;

    form.addEventListener('formdata', t.step_func(e => {
      assert_true(e.formData.has('file'));
      assert_equals(e.formData.get('file'), file);
      assert_true(e.formData.has('empty'));
      assert_true(e.formData.get('empty') instanceof File);
    }));
    form.submit();
  }, `Files in a ${enctype} for