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https://github.com/mpashkovskiy/ethereum-bank-tests


https://github.com/mpashkovskiy/ethereum-bank-tests

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Bank example truffle tests

==========================



Repo contains truffle tests for contract from [Simple Bank Example](https://jarjuk.wordpress.com/2017/12/06/sbuilder-bank/)



Let's add method to check bank's balances to be able write assertments in tests:



```solidity

function getBalance(address aAddress) public constant returns(uint256) {

  return balances[aAddress];

}

```



Initial contract code is available in `contracts/Bank_0.sol`



Execute `truffle test` to see failing tests.



### Problem 0. Non-payable saveAccount method (not found by sbuilder-eth)



Before fixing logical errors in the contract we have to fix saveAccount() method.

Method saveAccount() is not payable so msg.value doesn't exist in the context.



* Warning throwed by Remix IDE

```

browser/Bank.sol:10:53: Warning: "msg.value" used in non-payable function. Do you want to add the "payable" modifier to this function?

      balances[msg.sender] = balances[msg.sender] + msg.value;

                                                    ^-------^

```

* Validated by test `test/Bank_0_saveAccount_not_payable.js`



Solution: add `payable` modifier to the method



### Problem 1. Non-payable consturctor (not found by sbuilder-eth)



Accordingly to section [3.4. Run 2 for setup3 – Find 1st Bug](https://jarjuk.wordpress.com/2017/12/06/sbuilder-bank/#orgheadline7) sbuilder-eth indicates that it is possible to call constructor and transfer some amount of ether. Unfortunately it is impossible as constructor is not payable.



* Remix IDE gives the same warning:

```

browser/Bank.sol:8:30: Warning: "msg.value" used in non-payable function. Do you want to add the "payable" modifier to this function?

      balances[msg.sender] = msg.value;

                             ^-------^

```

* Validated by `migrations/1516447849_deploy__bank_1.js`. Uncomment line 4 and run `truffle test` and as a result migration will fail with error: `Cannot send value to non-payable constructor`



Solution: add `payable` modifier to the constructor



### Problem 2. this.balance != Sum(this.balances) (found by sbuilder-eth)



*Important:* If problem 1. is not solved this problem doesn't exist!



In the same section [3.4. Run 2 for setup3 – Find 1st Bug](https://jarjuk.wordpress.com/2017/12/06/sbuilder-bank/#orgheadline7) stated:



`Error analysis: constructor does not update balances variable, and invariant Bank_promise is violated in Bank() constructor.`



There is internal variable for every contract called `balance`. It is updated every time somebody sends funds to a contract. So actual balance of the contract will be updated but this transaction will not be represented in the balances map



Validated by migration `migrations/1516449292_deploy__bank_2.js` which sends funds to contract during deployment and test `test/Bank_2_constructor_records_transaction.js`



Solution: add `balances[msg.sender] = msg.value;` to the constructor.



### Problem 3. Imposibility to fake origin address of transaction (not found by sbuilder-eth)



Section [4.2 Run 3 for setup3 – Find 2nd Bug](https://jarjuk.wordpress.com/2017/12/06/sbuilder-bank/#find-bug-2) states that it is possible to call `saveAccount()` with bank address. It is impossible as to use bank (contract) address we have to unlock bank (contract) account but we have no key and password to do so. Only contract can call `saveAccount()` with it's own address.



Validated by `test/Bank_3_saveAccount_recursive_funding_0.js`



Solution: add method `recursiveTransfer(uint amount)` to the contract which will transfer funds. Important notice: Remix IDE gives two warnings about the method:



* `Gas requirement of function Bank_4.recursiveTransfer() high: infinite. If the gas requirement of a function is higher than the block gas limit, it cannot be executed. Please avoid loops in your functions or actions that modify large areas of storage (this includes clearing or copying arrays in storage)`

* `browser/Bank_4.sol:18:5:Use of "this" for local functions: Never use this to call functions in the same contract, it only consumes more gas than normal local calls.`



### Problem 4. Possibility to send funds "recursively" (found by sbuilder-eth)



*Important:* If problem 3. is not solved this problem doesn't exist.

 

Validated by `test/Bank_4_saveAccount_recursive_funding_1.js`



### Summary



Final version of contract availabe in `contracts/Bank_Final.sol` and tests are in `test/Bank_Final_saveAccount_no_recursive_funding.js`.



Simplified but still valid version presented in `contracts/Bank_Final_Simple.sol`. The only difference between simplified version and initial contract is `payable` modifier for `saveAccount()` method.