Test that liquidating a position does not leave the protocol with less collateral than minimum debt value

PositionManager.TotalCollateralCannotBeLowerThanMinCollateral.t.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.19;

import { Fixed256x18 } from "@tempusfinance/tempus-utils/contracts/math/Fixed256x18.sol";
import { PositionManager } from "../contracts/PositionManager.sol";
import { IERC20Indexable } from "../contracts/Interfaces/IERC20Indexable.sol";
import { IRToken } from "../contracts/Interfaces/IRToken.sol";
import { PriceFeedTestnet } from "./mocks/PriceFeedTestnet.sol";
import { TestSetup } from "./utils/TestSetup.t.sol";
import { FlashMintLiquidator } from "../contracts/FlashMintLiquidator.sol";
import { MockAMM } from "./mocks/MockAMM.sol";

contract PositionManagerLiquidationTotalCollateralCannotBeLowerThanMinCollateralTest is TestSetup {
    using Fixed256x18 for uint256;

    uint256 public constant DEFAULT_PRICE = 200 * 1e18;

    PriceFeedTestnet public priceFeed;
    PriceFeedTestnet public priceFeed2;
    IRToken public rToken;
    IERC20Indexable public raftDebtToken;
    IERC20Indexable public raftDebtToken2;

    MockAMM public mockAmm;
    FlashMintLiquidator public liquidator;

    function setUp() public override {
        super.setUp();

        priceFeed = new PriceFeedTestnet();
        priceFeed2 = new PriceFeedTestnet();
        rToken = positionManager.rToken();

        positionManager.addCollateralToken(collateralToken, priceFeed, splitLiquidationCollateral);
        positionManager.addCollateralToken(collateralToken2, priceFeed2, splitLiquidationCollateral2);

        mockAmm = new MockAMM(collateralToken2, rToken, DEFAULT_PRICE);
        liquidator = new FlashMintLiquidator(positionManager, mockAmm, collateralToken2);

        (,raftDebtToken, ,,,,,,,) = positionManager.collateralInfo(collateralToken);
        (,raftDebtToken2, ,,,,,,,) = positionManager.collateralInfo(collateralToken2);

        collateralToken.mint(ALICE, 10e36);
        collateralToken.mint(BOB, 10e36);
        collateralToken.mint(CAROL, 10e36);
        collateralToken.mint(DAVE, 10e36);
        collateralToken.mint(EVE, 10e36);
        collateralToken.mint(FRANK, 10e36);

        collateralToken2.mint(ALICE, 10e36);
        collateralToken2.mint(BOB, 10e36);
        collateralToken2.mint(CAROL, 10e36);
        collateralToken2.mint(DAVE, 10e36);
        collateralToken2.mint(EVE, 10e36);
        collateralToken2.mint(FRANK, 10e36);

        priceFeed.setPrice(DEFAULT_PRICE);
    }

    event Debug(string name, uint256 value);

    function testLiquidateCollateralWhenOnlyOnePositionActive() public {
        // 1. Deposit high TVL on collateral 1
        // 2. Deposit min on collateral 2
        // 3. Deposit high on collateral 2
        // 4. Liquidate high collateral 2 
        // 5. Deposit new high collateral 2
        // 6. See what happens to you and them

        // 1. Deposit high TVL on collateral 1
        uint256 initialCR = 1.11e18;
        uint256 rToMint = 55.6 * 1e6 * 1e18; // 55.6m TVL according to defillama
        uint256 collateralAmount = rToMint.divUp(DEFAULT_PRICE).mulUp(initialCR);

        vm.startPrank(ALICE);
        collateralToken.approve(address(positionManager), collateralAmount);
        positionManager.managePosition(
            collateralToken,
            ALICE,
            collateralAmount,
            true, // collateral increase
            rToMint,
            true, // debt increase
            1e17,
            emptySignature
        );
        emit Debug("b4 raftDebtToken.balanceOf(ALICE)", raftDebtToken.balanceOf(ALICE));
        emit Debug("b4 rToken.balanceOf(ALICE)", rToken.balanceOf(ALICE));

        // 2. Deposit min on collateral 2
        vm.stopPrank();
        vm.startPrank(BOB);
        rToMint = splitLiquidationCollateral2.LOW_TOTAL_DEBT(); // mint minimum debt value (3000 R) using collateral 2
        collateralAmount = rToMint.divUp(DEFAULT_PRICE).mulUp(initialCR); // assuming collateral 2 price == collateral 1 price
        collateralToken2.approve(address(positionManager), collateralAmount);
        positionManager.managePosition(
            collateralToken2,
            BOB,
            collateralAmount,
            true, // collateral increase
            rToMint,
            true, // debt increase
            1e17,
            emptySignature
        );

        emit Debug("b4 raftDebtToken2.balanceOf(BOB)", raftDebtToken2.balanceOf(BOB));
        emit Debug("b4 rToken.balanceOf(BOB)", rToken.balanceOf(BOB));
        
        vm.stopPrank();

        // 3. Deposit high on collateral 2
        // last position cannot be liquidated, so we need a new one
        vm.startPrank(CAROL);
        rToMint = 10_000 * splitLiquidationCollateral2.LOW_TOTAL_DEBT(); // whale
        collateralAmount = rToMint.divUp(DEFAULT_PRICE).mulUp(initialCR); // assuming collateral 2 price == collateral 1 price
        collateralToken2.approve(address(positionManager), collateralAmount);
        positionManager.managePosition(
            collateralToken2,
            CAROL,
            collateralAmount,
            true, // collateral increase
            rToMint,
            true, // debt increase
            1e17,
            emptySignature
        );
        vm.stopPrank();

        emit Debug("b4 raftDebtToken2.balanceOf(CAROL)", raftDebtToken2.balanceOf(CAROL));
        emit Debug("b4 rToken.balanceOf(CAROL)", rToken.balanceOf(CAROL));
        

        // 4. Liquidate high collateral 2 
        // price drops to 1ETH:198R, reducing CAROL's ICR between 100% and 110%
        uint256 price = 198e18;
        priceFeed2.setPrice(price);

        vm.startPrank(ALICE);
        positionManager.liquidate(CAROL); // liquidate whale, greatly reducing collateral2 from protocol

        emit Debug("raftDebtToken.balanceOf(ALICE)", raftDebtToken.balanceOf(ALICE));
        emit Debug("rToken.balanceOf(ALICE)", rToken.balanceOf(ALICE));
        emit Debug("raftDebtToken2.balanceOf(BOB)", raftDebtToken2.balanceOf(BOB));
        emit Debug("rToken.balanceOf(BOB)", rToken.balanceOf(BOB));
        emit Debug("raftDebtToken2.balanceOf(CAROL)", raftDebtToken2.balanceOf(CAROL));
        emit Debug("rToken.balanceOf(CAROL)", rToken.balanceOf(CAROL));


        assertEq(raftDebtToken.balanceOf(CAROL), 0);

        vm.stopPrank();

        // 5. Deposit new high collateral 2
        // another user tries to deposit again
        rToMint = 400_000e18;
        collateralAmount = rToMint.divUp(price).mulUp(initialCR);


        vm.startPrank(DAVE);
        collateralToken2.approve(address(positionManager), collateralAmount);
        positionManager.managePosition(
            collateralToken2,
            DAVE,
            collateralAmount,
            true, // collateral increase
            rToMint,
            true, // debt increase
            1e17,
            emptySignature
        );


        emit Debug("raftDebtToken2.balanceOf(DAVE)", raftDebtToken2.balanceOf(DAVE));
        emit Debug("rToken.balanceOf(DAVE)", rToken.balanceOf(DAVE));

        // 6. See what happens to you and them
        assertEq(raftDebtToken2.balanceOf(DAVE), rToken.balanceOf(DAVE));       
    }
}