- Added tests to cover flashLoan().

contracts/mocks/flashloan/MockFlashLoanReceiver.sol

@@ -18,12 +18,21 @@ contract MockFlashLoanReceiver is FlashLoanReceiverBase {
   event ExecutedWithFail(address _reserve, uint256 _amount, uint256 _fee);
   event ExecutedWithSuccess(address _reserve, uint256 _amount, uint256 _fee);
 
-  bool failExecution = false;
+  bool _failExecution;
+  uint256 _amountToApprove;
 
   constructor(ILendingPoolAddressesProvider provider) public FlashLoanReceiverBase(provider) {}
 
-  function setFailExecutionTransfer(bool _fail) public {
-    failExecution = _fail;
+  function setFailExecutionTransfer(bool fail) public {
+    _failExecution = fail;
+  }
+
+  function setAmountToApprove(uint256 amountToApprove) public {
+    _amountToApprove = amountToApprove;
+  }
+
+  function amountToApprove() public view returns (uint256) {
+    return _amountToApprove;
   }
 
   function executeOperation(
@@ -36,12 +45,11 @@ contract MockFlashLoanReceiver is FlashLoanReceiverBase {
     MintableERC20 token = MintableERC20(reserve);
 
     //check the contract has the specified balance
-    require(
-      amount <= IERC20(reserve).balanceOf(address(this)),
-      'Invalid balance for the contract'
-    );
+    require(amount <= IERC20(reserve).balanceOf(address(this)), 'Invalid balance for the contract');
 
-    if (failExecution) {
+    uint256 amountToReturn = (_amountToApprove != 0) ? _amountToApprove : amount.add(fee);
+
+    if (_failExecution) {
       emit ExecutedWithFail(reserve, amount, fee);
       return;
     }
@@ -51,7 +59,7 @@ contract MockFlashLoanReceiver is FlashLoanReceiverBase {
 
     token.mint(fee);
 
-    IERC20(reserve).approve(_addressesProvider.getLendingPool(), amount.add(fee));
+    IERC20(reserve).approve(_addressesProvider.getLendingPool(), amountToReturn);
 
     emit ExecutedWithSuccess(reserve, amount, fee);
   }

test/flashloan.spec.ts

@@ -282,4 +282,64 @@ makeSuite('LendingPool FlashLoan function', (testEnv: TestEnv) => {
 
     expect(callerDebt.toString()).to.be.equal('500450000', 'Invalid user debt');
   });
+
+  it('Caller deposits 5 ETH as collateral, Takes a USDC flashloan, approves only partially funds. A loan for caller is created', async () => {
+    const {usdc, pool, weth, users} = testEnv;
+
+    const caller = users[3];
+
+    await weth.connect(caller.signer).mint(await convertToCurrencyDecimals(weth.address, '5'));
+
+    await weth.connect(caller.signer).approve(pool.address, APPROVAL_AMOUNT_LENDING_POOL);
+
+    const amountToDeposit = await convertToCurrencyDecimals(weth.address, '5');
+
+    await pool.connect(caller.signer).deposit(weth.address, amountToDeposit, '0');
+
+    const flashloanAmount = await convertToCurrencyDecimals(usdc.address, '500');
+
+    await _mockFlashLoanReceiver.setFailExecutionTransfer(false);
+
+    await _mockFlashLoanReceiver.setAmountToApprove(flashloanAmount.div(2));
+    console.log((await _mockFlashLoanReceiver.amountToApprove()).toString());
+
+    await pool
+      .connect(caller.signer)
+      .flashLoan(_mockFlashLoanReceiver.address, usdc.address, flashloanAmount, 2, '0x10', '0');
+    const {variableDebtTokenAddress} = await pool.getReserveTokensAddresses(usdc.address);
+
+    const usdcDebtToken = await getContract<VariableDebtToken>(
+      eContractid.VariableDebtToken,
+      variableDebtTokenAddress
+    );
+
+    const callerDebt = await usdcDebtToken.balanceOf(caller.address);
+
+    expect(callerDebt.toString()).to.be.equal('250450000', 'Invalid user debt');
+  });
+
+  it('Caller deposits 1000 DAI as collateral, Takes WETH flashloan, does not return the funds and selects revert as result', async () => {
+    const {dai, pool, weth, users} = testEnv;
+
+    const caller = users[3];
+
+    await dai.connect(caller.signer).mint(await convertToCurrencyDecimals(dai.address, '1000'));
+
+    await dai.connect(caller.signer).approve(pool.address, APPROVAL_AMOUNT_LENDING_POOL);
+
+    const amountToDeposit = await convertToCurrencyDecimals(dai.address, '1000');
+
+    await pool.connect(caller.signer).deposit(dai.address, amountToDeposit, '0');
+
+    const flashAmount = ethers.utils.parseEther('0.8');
+
+    await _mockFlashLoanReceiver.setFailExecutionTransfer(false);
+    await _mockFlashLoanReceiver.setAmountToApprove(flashAmount.div(2));
+
+    await expect(
+      pool
+        .connect(caller.signer)
+        .flashLoan(_mockFlashLoanReceiver.address, weth.address, flashAmount, 0, '0x10', '0')
+    ).to.be.revertedWith('ERC20: transfer amount exceeds allowance');
+  });
 });