text: def requires_mdtraj(*args, **kwargs):  # pragma: no cover
      raise RuntimeError("This requires MDTraj, which is not installed")
  
  try:
      import mdtraj
  except ImportError:
      Engine = requires_mdtraj
      ExternalMDSnapshot = requires_mdtraj
  else:
      from .engine import GromacsEngine as Engine
      from .engine import ExternalMDSnapshot
  
  