code: def test_has_ref(self) -> None:
      prop0 = bcpr.Required(Int)
      assert not prop0.has_ref
      prop1 = bcpr.Required(Instance(_TestModel))
      assert prop1.has_ref
  
file_path: bokeh/tests/unit/bokeh/core/property/test_required.py
imports: from __future__ import annotations
  import pytest
  from bokeh.core.properties import Instance, Int, List
  from tests.support.util.api import verify_all
  from _util_property import _TestHasProps, _TestModel
  import bokeh.core.property.required
label_desc: Use image node_id 4 for calling the Test_Required obj's underlying member method code with example usage: obj.test_has_ref() without return types