Solidity-Fundamentals-Test

Hello! If you're reading this, you applied to a Solidity Engineering role at Coinocracy. This is Coinocracy's hiring test for Solidity engineers. (Note: If you have not applied but stumbled across this repository somehow, you are welcome to check out our job postings.)

When you fork this repository, you should make your fork private and share it with williamstarkro on Github with an admin role. By forking this repository, you agree to keep the MIT License intact and assign the MIT License to your fork as well.

In this repository, we have a very insecure vault located at Vault.sol. It can keep track of balances, handle deposits, and handle withdrawals for a single user. It essentially acts as a vault account for a single person and does not support multiple users at the moment. The vault receives a fee from that user for every withdrawal. As you work on Vault.sol, think about:

• What parts of Vault.sol need sanity checks?
• What parts of Vault.sol need to have access control or contain private information?
• What are values for variables in Vault.sol that should never occur?

Your primary task is to help secure Vault.sol. Some resources that may help:

• SafeMath by OpenZeppelin
• AccessControl by OpenZeppelin
• Solidity function modifiers
• Solidity error handling

Your optional secondary task (which is optional but will stand out significantly if you complete it) is to add a fee calculation to Vault.sol. The vault needs to receive a 0.3% fee on every withdrawal of DAI. This isn't as simple as it sounds! Solidity only supports math on integers. Therefore, you need everything to be in wei, which is the smallest unit for Ethereum. As an example, the DAI balance on Etherscan for the address 0xF977814e90dA44bFA03b6295A0616a897441aceC may be $25,039,869 (reported in ether by Etherscan), but its balance in daiContract.methods.balanceOf(daiWhale).call() is 25035868999999999999995000 (reported in wei by web3.js). This token division is represented in decimals, which is a property available in ERC20.sol. Note that DAI has 18 decimals (the default). For more, take a look at the Solidity docs on units and division.

If you really want to go above and beyond with an optional tertiary task, you can modify Vault.sol to support multiple users. The Vault.sol contract only supports a single user at the moment, but handling deposits and withdrawals for multiple users would stand out significantly and greatly exceed our expectations.

This project is well compensated to give you the time you need to properly secure Vault.sol and work on the optional tasks. The more thorough you are in ensuring the contract's security and completing the optional tasks, the better you'll perform.

Setup Instructions

1. Install required packages with yarn install
2. Run npm compile to compile the contracts and create the documentation
3. Run npm test to run the tests
4. The initial tests should pass for depositToVault and withdrawFromVault and fail for calculateVaultFee.