Compound V3 Rebasing Test

comet.t.sol

pragma solidity ^0.8.13;

import "forge-std/Test.sol";
import "forge-std/console2.sol";

interface IComet {
  function supply(address asset, uint amount) virtual external;
  function balanceOf(address owner) virtual external view returns (uint256);
}

interface IERC20 {
  function approve(address spender, uint256 amount) external returns (bool);

}

contract CometTest is Test {
  IComet public comet = IComet(0xc3d688B66703497DAA19211EEdff47f25384cdc3);
  IERC20 public constant USDC = IERC20(0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48);

  function testFork_BalanceInterestAccrual() public {
    vm.createSelectFork(
      "https://mainnet.infura.io/v3/xxxxx",
      16579384
    );

    address alice = makeAddr('alice');
    address bob = makeAddr('bob');

    deal(address(USDC), alice, 1 ether);
    deal(address(USDC), bob, 1 ether);

    assertEq(comet.balanceOf(alice), 0);
    assertEq(comet.balanceOf(bob), 0);

    vm.startPrank(alice);
    USDC.approve(address(comet), type(uint).max);
    comet.supply(address(USDC), 1 ether);
    vm.stopPrank();

    assertEq(comet.balanceOf(alice), 1 ether - 1);
    assertEq(comet.balanceOf(bob), 0);

    vm.warp(block.timestamp + 60*60*24*365); // a year

    // Alice's balance should have increased w/ the passing of time.
    assertGt(comet.balanceOf(alice), 1 ether - 1);
    assertEq(comet.balanceOf(bob), 0);

    vm.startPrank(bob);
    USDC.approve(address(comet), type(uint).max);
    comet.supply(address(USDC), 1 ether);
    vm.stopPrank();

    console2.log("alice balance", comet.balanceOf(alice));
    console2.log("bob balance", comet.balanceOf(bob));
    
    assertGt(
      comet.balanceOf(alice),
      comet.balanceOf(bob)
    );
  }
}