code: def test_widget_no_data(self):
      widget = PerspectiveWidget(None, plugin="X Bar", group_by=["a"])
      assert widget.plugin == "X Bar"
      assert widget.group_by == ["a"]
  
imports: from datetime import date, datetime
  from functools import partial
  from types import MethodType
  import numpy
  from perspective import PerspectiveError, PerspectiveWidget, Table
  from pytest import raises
label_desc: Use image node_id 3 for calling the TestWidget obj's underlying member method code with example usage: obj.test_widget_no_data() without return types