code: def validate_accounting_equation(cls):
          
          balances = [account.balance(raw=True) for account in Account.objects.root_nodes()]
          if sum(balances, Balance()) != 0:
              raise exceptions.AccountingEquationViolationError(
                  "Account balances do not sum to zero. They sum to {}".format(sum(balances))
              )
docs: Check that all accounts sum to 0