code: def which(self, cmd: str) -> str:
      assert self.bin.exists()
      return shutil.which(cmd, path=self.bin) or cmd
  
imports: import os
  import shutil
  from pathlib import Path
  from subprocess import check_output
  from typing import Dict, Optional
  import pytest
  from dulwich.porcelain import clone
  from funcy import first
  from packaging import version
  from dvc.types import StrPath
label_desc: Use image node_id 4 for calling the VirtualEnv obj's underlying member method code with example usage: obj.which(cmd) and returns: unknown