code: func (cmd *cmdWrapper) CombinedOutput() ([]byte, error) {
  	out, err := (*osexec.Cmd)(cmd).CombinedOutput()
  	if err != nil {
  		if ee, ok := err.(*osexec.ExitError); ok {
  			// Force a compile fail if exitErrorWrapper can't convert to ExitError.
  			var x ExitError = &exitErrorWrapper{ee}
  			return out, x
  		}
  		if ee, ok := err.(*osexec.Error); ok {
  			if ee.Err == osexec.ErrNotFound {
  				return out, ErrExecutableNotFound
  			}
  		}
  		return out, err
  	}
  	return out, nil
  }
docs: // CombinedOutput is part of the Cmd interface.