code: def eth_getBalance(self, address=None, block=BLOCK_TAG_LATEST):
          
          address = address or self.eth_coinbase()
          block = validate_block(block)
          return hex_to_dec(self._call("eth_getBalance", [address, block]))
docs: TODO: documentation
  
          https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_getbalance
  
          TESTED