code: def test__delitem__removes_existing_key(self):
      del self.query_params["foo"]
      assert "foo" not in self.query_params
      message = self.get_message_from_queue(0)
      assert "two=x&two=y" in message.page_info_changed.query_string
      assert "foo" not in message.page_info_changed.query_string
  
imports: import pytest
  from streamlit.errors import StreamlitAPIException
  from streamlit.runtime.state.query_params import QueryParams
  from tests.delta_generator_test_case import DeltaGeneratorTestCase
label_desc: Use image node_id 21 for calling the QueryParamsMethodTests obj's underlying member method code with example usage: obj.test__delitem__removes_existing_key() without return types