updated TestToken to include approveAndCall like SNT contract

contracts/token/ApprovalReceiver.sol

@@ -0,0 +1,5 @@
+pragma solidity ^0.4.11;
+
+contract ApprovalReceiver {
+  function receiveApproval(address from, uint value, address tokenContract, bytes extraData) returns (bool);
+}

contracts/token/StandardToken.sol

@@ -20,14 +20,23 @@ contract StandardToken is ERC20Token {
         return transfer(msg.sender, _to, _value);
     }
 
-    function approve(address _spender, uint256 _value) 
-        external
-        returns (bool success) 
-    {
-        allowed[msg.sender][_spender] = _value;
-        emit Approval(msg.sender, _spender, _value);
-        return true;
-    }
+    /**
+     * @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender.
+     * @param _spender The address which will spend the funds.
+     * @param _value The amount of tokens to be spent.
+     */
+    function approve(address _spender, uint256 _value) returns (bool) {
+
+      // To change the approve amount you first have to reduce the addresses`
+      //  allowance to zero by calling `approve(_spender, 0)` if it is not
+      //  already 0 to mitigate the race condition described here:
+      //  https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
+      require((_value == 0) || (allowed[msg.sender][_spender] == 0));
+
+      allowed[msg.sender][_spender] = _value;
+      Approval(msg.sender, _spender, _value);
+      return true;
+  }
 
     function transferFrom(
         address _from,

contracts/token/TestToken.sol

@@ -1,6 +1,7 @@
 pragma solidity ^0.4.23;
 
 import "./StandardToken.sol";
+import './ApprovalReceiver.sol';
 
 /**
  * @notice ERC20Token for test scripts, can be minted by anyone.
@@ -16,4 +17,10 @@ contract TestToken is StandardToken {
     function mint(uint256 _amount) public {
         mint(msg.sender, _amount);
     }
+
+    function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) {
+      assert(approve(_spender, _value));
+      return ApprovalReceiver(_spender).receiveApproval(msg.sender, _value, this, _extraData);
+    }
+
 }