class_docstr: Useful commands
  - run all tests: pytest examples/orderbook_data/example.py
  - run a single test:  pytest -s --pdb --disable-warnings examples/orderbook_data/example.py::TestClass::test_basic01
class_docstr_tok: ["Useful","commands","-","run","all","tests",":","pytest","examples\/orderbook_data\/example.py","-","run","a","single","test",":","pytest","-s","--","pdb","--","disable-warnings","examples\/orderbook_data\/example.py",":",":TestClass",":",":test_basic01"]
code: def test_exp_05(self):
      exprs = [
          f"2 * Sub({ self.total_func('ask', 'last')}, {self.total_func('bid', 'last')})/{self.expr_sum_buy_ask_1}",
          f"Sub({ self.total_func('asize', 'mean')}, {self.total_func('bsize', 'mean')})/{self.total_volume}",
      ]
      names = ["p_accspread", "v_accspread"]
  
      df = D.features(self.stocks_list, fields=exprs, freq="ticks")
      df.columns = names
      print(df)
  
imports: from arctic.arctic import Arctic
  import qlib
  from qlib.data import D
  import unittest
label_desc: Use image node_id 12 for calling the TestClass obj's underlying member method code with example usage: obj.test_exp_05() without return types