function test_POC_WrongDecimals() public {
    uint256 _wbtcAmount = 3e8; // 3 BTC
    address _user = makeAddr("user");
    _mintPool(_user, WBTC, _wbtcAmount);
    uint256 _wbtcDecimals = 1e8;
    uint256 VIRTUAL_SHARES = 1e8;
    uint256 _poolDecimals = 10**lendingPools[WBTC].decimals();
    uint256 _userBalance = lendingPools[WBTC].balanceOf(_user);
    assertEq(_userBalance/_poolDecimals, _wbtcAmount/_wbtcDecimals*VIRTUAL_SHARES);
    assertEq(_userBalance/_poolDecimals, 3e8);
    assertEq(_userBalance, _wbtcAmount*VIRTUAL_SHARES);
}
uint private constant VIRTUAL_SHARES = 8;
...
function decimals() public view override returns (uint8) {
    return IERC20Metadata(underlyingToken).decimals() + VIRTUAL_SHARES;
}
...
function _toShares(uint _amt, uint _totalAssets, uint _totalShares) internal pure returns (uint shares) {
    return _amt.mulDiv(_totalShares + 10**VIRTUAL_SHARES, _totalAssets + VIRTUAL_ASSETS);
}
...
function _toAmt(uint _shares, uint _totalAssets, uint _totalShares) internal pure returns (uint amt) {
    return _shares.mulDiv(_totalAssets + VIRTUAL_ASSETS, _totalShares + 10**VIRTUAL_SHARES);
}
