Lesson 12 - Can't write test for DSCMint function

[smahdi-dev]

I want to write a test for a situation in which user wants to mint DSCs more than collateral.
the following code is mintDSC function and _revertIfHealthFactorIsBroken functions:

    function mintDSC(uint256 amountDscToMint) public moreThanZero(amountDscToMint) {
        s_DSCMinted[msg.sender] += amountDscToMint;
        _revertIfHealthFactorIsBroken(msg.sender);

        bool minted = i_dsc.mint(msg.sender, amountDscToMint);
        if (!minted) {
            revert DSCEngine__MintFailed();
        }
    }

    function _revertIfHealthFactorIsBroken(address user) internal view {
        uint256 userHealthFactor = _healthFactor(user);
        if (userHealthFactor < MIN_HEALTH_FACTOR) {
            revert DSCEngine__BreaksHealthFactor(userHealthFactor);
        }
    }

the problem lies in DSCEngine__BreaksHealthFactor(userHealthFactor); custom error which has a parameter.
look at the following code showing my test:

    function testMintRevertsIfHealthFactorIsBroken() public depositedCollateral {
        vm.startPrank(USER);
        vm.expectRevert(abi.encodeWithSelector(DSCEngine.DSCEngine__BreaksHealthFactor, ??));
        engine.mintDSC(100000);
        vm.stopPrank();
    }

what value should i give to the custom error in vm.expectRevert(abi.encodeWithSelector(DSCEngine.DSCEngine__BreaksHealthFactor, ??)); instead of ??. the problem is that I have to call getHealthFactor after engine.mintDSC(100000); to calculate changes but I need what getHealthFactor returns before calling expectRevert to fill ?? section.

or mkae me aware if i am doing it the wrong way.

[EngrPips]

Hello @smahdi-dev, You can just use vm.expectRevert() without trying to pass in the exact data you are expecting to revert. Or you can maybe have some utility function that would calculate a user's health factor based on how much DSC they want to mint without actually minting any DSC.

[EngrPips]

How much does the user deposits in your depositedCollateral modifier ?

[smahdi-dev]

Hi bro @EngrPips , I think I am doing the same. and i am depositing 10 ether. look:

uint256 public constant AMOUNT_COLLATERAL = 10 ether;

    modifier depositedCollateral() {
        vm.startPrank(USER);
        ERC20Mock(weth).approve(address(engine), AMOUNT_COLLATERAL);
        engine.depositCollateral(weth, AMOUNT_COLLATERAL);
        vm.stopPrank();
        _;
    }

    function testMintRevertsIfHealthFactorIsBroken() public depositedCollateral {
        vm.startPrank(USER);
        vm.expectRevert();
        engine.mintDSC(10 ether);
        vm.stopPrank();
    }

[EngrPips]

If you run this test, you just showed me it should pass.

[smahdi-dev]

unfortunately, I'm still getting the error [FAIL. Reason: call did not revert as expected].

could you please take a look at the code. https://github.com/smahdi-dev/defi-stablecoin

[EngrPips]

Alright, I will take a look and let you know whatever I find as soon as possible.

[EngrPips]

Hello @smahdi-dev, Below is your _healthFactor function. Why did you multiply collateralAdjustedForThreshold by PRECISION in the line below

return (collateralAdjustedForThreshold * PRECISION) / totalDscMinted;

function _healthFactor(address user) internal view returns (uint256) {
        // total DSC minted
        // total collateral value
        (uint256 totalDscMinted, uint256 collateralValueInUsd) = _getAccountInformation(user);
        if (collateralValueInUsd == 0) {
            revert DSCEngine__NoCollateralDeposited();
        }
        if (totalDscMinted == 0) {
            revert DSCEngine__NoDscMinted();
        }
        uint256 collateralAdjustedForThreshold = (collateralValueInUsd * LIQUIDATION_THRESHOLD) / LIQUIDATION_PRECISION;
        return (collateralAdjustedForThreshold * PRECISION) / totalDscMinted;
    }

Below is mine

function _health_factor(address _user) internal view returns (uint256 health_factor) {
        (uint256 total_DSC_minted, uint256 collateral_value_in_USD) = _get_account_information(_user);
        console2.log("the total collateral value in usd is: ", collateral_value_in_USD);
        console2.log("the total DSC minted is: ", total_DSC_minted);
        if (total_DSC_minted == 0) return type(uint256).max;
        uint256 collateral_amount_for_threshold =
            (collateral_value_in_USD * LIQUIDATION_THRESHOLD) / LIQUIDATION_THRESHOLD_DIVIDER;
        console2.log("the collateral amount for threshold is: ", collateral_amount_for_threshold);
        health_factor = collateral_amount_for_threshold  / total_DSC_minted;
        console2.log("the calculated health factor is: ", health_factor);
        return health_factor;
    }

Maybe Patrick multiplied it in his codebase, and it worked for him, but when I ran into an issue and what the tutor did in the tutorial didn't work, I came back to thinking and figuring out how it would work for me. What a programmer does is figure out stuff.

[smahdi-dev]

@EngrPips , I removed PRECISION and it worked.
as you said Patrick did it in the course.
and I also wanted to say that I have trouble understanding these math stuff because solidity doesn't support decimals, it always confuses me and I don't know when to add 1e18? sometimes Patrick adds 1e10 or 1e8.

how can i understand it better?

[EngrPips]

Hello @smahdi-dev, It is very typical that you find it difficult to understand solidity mathematics when you are just starting out with solidity, but with time, it will make more sense, and naturally, you will feel comfortable with it. I expect that you will run into another issue when you try to test that the DSCEngine properly mints DSC without the user breaking their health_factor. When that happens, make sure to reach out here.

[smahdi-dev]

thanks for the help ❤️ @EngrPips

[EngrPips]

I am glad I could help.