Fixes tests on flashloans

contracts/flashloan/base/FlashLoanReceiverBase.sol

@@ -6,6 +6,7 @@ import '@openzeppelin/contracts/token/ERC20/IERC20.sol';
 import '../interfaces/IFlashLoanReceiver.sol';
 import '../../interfaces/ILendingPoolAddressesProvider.sol';
 import '../../libraries/UniversalERC20.sol';
+import '@nomiclabs/buidler/console.sol';
 
 abstract contract FlashLoanReceiverBase is IFlashLoanReceiver {
   using UniversalERC20 for IERC20;
@@ -32,12 +33,6 @@ abstract contract FlashLoanReceiverBase is IFlashLoanReceiver {
     address _reserve,
     uint256 _amount
   ) internal {
-    if (IERC20(_reserve).isETH()) {
-      //solium-disable-next-line
-      _destination.call{value: _amount}('');
-      return;
-    }
-
     IERC20(_reserve).universalTransfer(_destination, _amount);
   }
 

contracts/lendingpool/LendingPool.sol

@@ -710,7 +710,11 @@ contract LendingPool is ReentrancyGuard, VersionedInitializable {
       vars.protocolFee
     );
 
-    IERC20(_reserve).universalTransfer(addressesProvider.getTokenDistributor(), vars.protocolFee);
+    //transfer funds to the receiver
+    AToken(vars.aTokenAddress).transferUnderlyingTo(
+      addressesProvider.getTokenDistributor(),
+      vars.protocolFee
+    );
 
     //solium-disable-next-line
     emit FlashLoan(_receiver, _reserve, _amount, vars.amountFee, vars.protocolFee, block.timestamp);

contracts/mocks/flashloan/MockFlashLoanReceiver.sol

@@ -50,8 +50,10 @@ contract MockFlashLoanReceiver is FlashLoanReceiverBase {
     if (!IERC20(_reserve).isETH()) {
       token.mint(_fee);
     }
+
     //returning amount + fee to the destination
     transferFundsBackInternal(_reserve, _destination, _amount.add(_fee));
+
     emit ExecutedWithSuccess(_reserve, _amount, _fee);
   }
 }

contracts/tokenization/AToken.sol

@@ -639,15 +639,30 @@ contract AToken is ERC20 {
     }
   }
 
-  function transferUnderlyingTo(address _user, uint256 _amount)
+  /**
+   * @dev transfers the underlying asset to the target. Used by the lendingpool to transfer
+   * assets in borrow(), redeem() and flashLoan()
+   * @param _target the target of the transfer
+   * @param _amount the amount to transfer
+   * @return the amount transferred
+   **/
+
+  function transferUnderlyingTo(address _target, uint256 _amount)
     external
     onlyLendingPool
     returns (uint256)
   {
-    ERC20(underlyingAssetAddress).universalTransfer(_user, _amount);
+    ERC20(underlyingAssetAddress).universalTransfer(_target, _amount);
+    return _amount;
   }
 
-  receive() external payable{
-      require(ERC20(underlyingAssetAddress).isETH(), "Transfers are only allowed if the underlying asset is ETH");
+  /**
+   * @dev receive() function for aTokens who hold ETH as the underlying asset
+   **/
+  receive() external payable {
+    require(
+      ERC20(underlyingAssetAddress).isETH(),
+      'Transfers are only allowed if the underlying asset is ETH'
+    );
   }
 }