Create _setCurrentContextAddressIfRequired function in MixinTransactions

contracts/exchange/contracts/src/MixinTransactions.sol

@@ -99,11 +99,9 @@ contract MixinTransactions is
             transactionHash
         );
 
-        address signerAddress = transaction.signerAddress;
-        if (signerAddress != msg.sender) {
         // Set the current transaction signer
-            currentContextAddress = signerAddress;
-        }
+        address signerAddress = transaction.signerAddress;
+        _setCurrentContextAddressIfRequired(signerAddress);
 
         // Execute transaction
         transactionsExecuted[transactionHash] = true;
@@ -116,9 +114,7 @@ contract MixinTransactions is
         }
 
         // Reset current transaction signer if it was previously updated
-        if (signerAddress != msg.sender) {
-            currentContextAddress = address(0);
-        }
+        _setCurrentContextAddressIfRequired(address(0));
 
         emit TransactionExecution(transactionHash);
 
@@ -190,6 +186,16 @@ contract MixinTransactions is
         }
     }
 
+    /// @dev Sets the currentContextAddress if the current context is not msg.sender.
+    /// @param contextAddress The current context address.
+    function _setCurrentContextAddressIfRequired(address contextAddress)
+        internal
+    {
+        if (contextAddress != msg.sender) {
+            currentContextAddress = contextAddress;
+        }
+    }
+
     /// @dev The current function will be called in the context of this address (either 0x transaction signer or `msg.sender`).
     ///      If calling a fill function, this address will represent the taker.
     ///      If calling a cancel function, this address will represent the maker.

contracts/exchange/contracts/test/TestTransactions.sol

@@ -49,6 +49,12 @@ contract TestTransactions is
         transactionsExecuted[hash] = true;
     }
 
+    function setCurrentContextAddressIfRequired(address context)
+        external
+    {
+        _setCurrentContextAddressIfRequired(context);
+    }
+
     function getCurrentContextAddress()
         external
         view

contracts/exchange/test/transactions_unit_tests.ts

@@ -692,6 +692,22 @@ blockchainTests.resets('Transaction Unit Tests', ({ provider, web3Wrapper, txDef
         });
     });
 
+    describe('setCurrentContextAddressIfRequired', () => {
+        it('should set the currentContextAddress if not equal to sender', async () => {
+            const randomAddress = hexRandom(20);
+            await transactionsContract.setCurrentContextAddressIfRequired.awaitTransactionSuccessAsync(randomAddress);
+            const currentContextAddress = await transactionsContract.currentContextAddress.callAsync();
+            expect(currentContextAddress).to.eq(randomAddress);
+        });
+        it('should not set the currentContextAddress if equal to sender', async () => {
+            await transactionsContract.setCurrentContextAddressIfRequired.awaitTransactionSuccessAsync(accounts[0], {
+                from: accounts[0],
+            });
+            const currentContextAddress = await transactionsContract.currentContextAddress.callAsync();
+            expect(currentContextAddress).to.eq(constants.NULL_ADDRESS);
+        });
+    });
+
     describe('getCurrentContext', () => {
         it('should return the sender address when there is not a saved context address', async () => {
             const currentContextAddress = await transactionsContract.getCurrentContextAddress.callAsync({