code: def _run_time_check():
      """Return True if run-time support for Hexagon is present, otherwise
      error string.
  
      Designed for use as a the ``run_time_check`` argument to
      `tvm.testing.Feature`.
      """
      if ANDROID_SERIAL_NUMBER not in os.environ:
          return (
              f"Missing environment variable {ANDROID_SERIAL_NUMBER}."
          )
  
      return True
  
imports: import os
  import tvm
label_desc: Use image node_id 2 for calling a global function with example usage: _run_time_check() and returns: True, str, ANDROID_SERIAL_NUMBER, str