new_contents: #!/usr/bin/env python3
  # Copyright (c) 2019 The Bitcoin Core developers
  # Distributed under the MIT software license, see the accompanying
  # file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  from test_framework.test_framework import BitcoinTestFramework
  
  class TestShell:
      """Wrapper Class for BitcoinTestFramework.
  
      The TestShell class extends the BitcoinTestFramework
      rpc & daemon process management functionality to external
      python environments.
  
      It is a singleton class, which ensures that users only
      start a single TestShell at a time."""
  
      class __TestShell(BitcoinTestFramework):
          def set_test_params(self):
              pass
  
          def run_test(self):
              pass
  
          def setup(self, **kwargs):
              if self.running:
                  print("TestShell is already running!")
                  return
  
              # Num_nodes parameter must be set
              # by BitcoinTestFramework child class.
              self.num_nodes = kwargs.get('num_nodes', 1)
              kwargs.pop('num_nodes', None)
  
              # User parameters override default values.
              for key, value in kwargs.items():
                  if hasattr(self, key):
                      setattr(self, key, value)
                  elif hasattr(self.options, key):
                      setattr(self.options, key, value)
                  else:
                      raise KeyError(key + " not a valid parameter key!")
  
              super().setup()
              self.running = True
  
          def shutdown(self):
              if not self.running:
                  print("TestShell is not running!")
              else:
                  super().shutdown()
                  self.running = False
  
          def reset(self):
              if self.running:
                  print("Shutdown TestWrapper before resetting!")
              else:
                  self.num_nodes = None
                  super().__init__()
  
      instance = None
  
      def __new__(cls):
          # This implementation enforces singleton pattern, and will return the
          # previously initialized instance if available
          if not TestShell.instance:
              TestShell.instance = TestShell.__TestShell()
              TestShell.instance.running = False
          return TestShell.instance
  
      def __getattr__(self, name):
          return getattr(self.instance, name)
  
      def __setattr__(self, name, value):
          return setattr(self.instance, name, value)
  
subject: Add TestShell class