Lottery: testing test_get_entrance_fee() fails

[pavelgor84]

Hi! I reached the first test for entrance fee function and have an error during testing this script:

**from brownie import Lottery, accounts, network, config
from web3 import Web3

def test_get_entrance_fee():
account = accounts[0]
lottery = Lottery.deploy(
config["networks"][network.show_active()]["eth_usd_price_feed"],
{"from": account},
)

assert lottery.getEntranceFee() > Web3.toWei(0.010, "ether")
assert lottery.getEntranceFee() < Web3.toWei(0.013, "ether")**

ERROR:

  assert lottery.getEntranceFee() > Web3.toWei(0.010, "ether")

E AssertionError: assert 0 > 10000000000000000
E + where 0 = <ContractCall 'getEntranceFee()'>()
E + where <ContractCall 'getEntranceFee()'> = <Lottery Contract '0xE7eD6747FaC5360f88a2EFC03E00d25789F69291'>.getEntranceFee
E + and 10000000000000000 = <function to_wei at 0x7fd9e59173a0>(0.01, 'ether')
E + where <function to_wei at 0x7fd9e59173a0> = Web3.toWei

tests/test_lottery.py:12: AssertionError
============================================== short test summary info ==============================================
FAILED tests/test_lottery.py::test_get_entrance_fee - AssertionError: assert 0 > 10000000000000000
================================================= 1 failed in 9.38s

It seems that test_get_entrance_fee() returns a number with floating point that raises the error " assert 0 > 10000000000000000". But on the video this test is passing.
My config:
etworks:
mainnet-fork:
eth_usd_price_feed: '0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419'

[cromewar]

Hello @pavelgor84 it seems your getEntranceFee function might be the error, if you check the return statement for the function is uint256 it means it cannot have a floating point. As you can see it says 0 > 1000000000000000, this means your getEntranceFee is returning 0.. I have some recommendations for you:

1. Make sure your contract looks like this: Special attention to the commas on (, int256 price, , , )

import "@chainlink/contracts/src/v0.6/interfaces/AggregatorV3Interface.sol";
AggregatorV3Interface internal ethUsdPriceFeed;
  function getEntranceFee() public view returns (uint256) {
        (, int256 price, , , ) = ethUsdPriceFeed.latestRoundData();
        // set entrance fee to $50
        // Eth/Usd conversion has 8 decimals so in order to make it 18 (wei standard) it's necessary to multiply the price.
        uint256 adjustedPrice = uint256(price) * (10**10); //18 decimals
        uint256 costToEnter = (usdEntryFee * 10**18) / adjustedPrice;
        return costToEnter;
    }

2. Don't forget to setup the network properly with alchemy: video timestamp 6:28:10
3. I'm going to suppose you just made a typo here:
   
   nut make sure your brownie-config.yaml is correct.

I hope this info might help you.

[pavelgor84]

Thanks for answering, @cromewar !
Here my function :

import "@chainlink/contracts/src/v0.6/interfaces/AggregatorV3Interface.sol";
constructor(address _priceFeedAddress) public {
uint256 usdEntryFee = 50 * (10**18);
ethUsdPriceFeed = AggregatorV3Interface(_priceFeedAddress);
}

function getEntranceFee() public view returns (uint256) {
    (, int256 price, , , ) = ethUsdPriceFeed.latestRoundData();
    uint256 adjustedPrice = uint256(price) * 10**10; // 18 decimals (8 +10)
    // 50$, 2000 / ETH
    // 50 * 100000 / 2000
    uint256 costToEnter = (usdEntryFee * 10**18) / adjustedPrice;
    return costToEnter;
}

And config file:
dependencies:

• smartcontractkit/[email protected]

compiler:
solc:
remappings:
- '@chainlink=smartcontractkit/[email protected]'

networks:
mainnet-fork:
eth_usd_price_feed: '0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419'

When I'm modifying this function to return just this int256 price, it shows me 436663268438. I made it via console.
But when I change everything back, it shows me 0🤯

[cromewar]

I found the error and I have the explanation as well:

Look this, you declare the variable usdEntryFeelike this:

uint256 usdEntryFee = 50 * (10**18);

and then on your function you set costToEnter like this:

uint256 costToEnter = (usdEntryFee * 10**18) / adjustedPrice;

As you can see you are multiplying usdEntryFee twice which gives you a giant number I can't even describe.

So, uint256 has a maximum space capacity of 256 bytes, when you exceed that amount it would or restart or return 0, this is why you are getting the error.

Solution:

Change: uint256 usdEntryFee = 50 * (10**18);
to this: uint256 public usdEntryFee;

[pavelgor84]

I found an issue. "uint256 public usdEntryFeel;" has already been declared above the constructor and I added uint256 to this variable in the constructor. This caused an error!
Thanks @cromewar! You moved me on the right path!

[cromewar]

I'm glad it helped, remember don't multiply twice as well, I you have any other question feel free to ask.