code: func (b *SimulatedBackend) PendingNonceAt(ctx context.Context, account common.Address) (uint64, error) {
  	b.mu.Lock()
  	defer b.mu.Unlock()
  
  	return b.pendingState.GetOrNewStateObject(account).Nonce(), nil
  }
docs: // PendingNonceAt implements PendingStateReader.PendingNonceAt, retrieving
  // the nonce currently pending for the account.