code: func NewMockIdentityManager(opts ...UsersOption) msp.IdentityManager {
  
  	manager := MockIdentityManager{}
  
  	usersOptions := UsersOptions{}
  
  	for _, param := range opts {
  		err := param(&usersOptions)
  		if err != nil {
  			panic(fmt.Errorf("failed to create IdentityManager: %s", err))
  		}
  	}
  	if usersOptions.users != nil {
  		manager.users = usersOptions.users
  	} else {
  		manager.users = make(map[string]msp.SigningIdentity)
  	}
  
  	return &manager
  }
docs: // NewMockIdentityManager Constructor for a identity manager.