add safe ERC20 helpers

test/helpers/SafeERC20Helper.sol

@@ -0,0 +1,48 @@
+pragma solidity ^0.4.11;
+
+import '../../contracts/token/ERC20.sol';
+import '../../contracts/token/SafeERC20.sol';
+
+contract ERC20FailingMock is ERC20 {
+  function transfer(address, uint256) returns (bool) {
+    return false;
+  }
+
+  function transferFrom(address, address, uint256) returns (bool) {
+    return false;
+  }
+
+  function approve(address, uint256) returns (bool) {
+    return false;
+  }
+
+  function balanceOf(address) constant returns (uint256) {
+    return 0;
+  }
+
+  function allowance(address, address) constant returns (uint256) {
+    return 0;
+  }
+}
+
+contract SafeERC20Helper {
+  using SafeERC20 for ERC20;
+
+  ERC20 token;
+
+  function SafeERC20Helper() {
+    token = new ERC20FailingMock();
+  }
+
+  function doFailingTransfer() {
+    token.safeTransfer(0, 0);
+  }
+
+  function doFailingTransferFrom() {
+    token.safeTransferFrom(0, 0, 0);
+  }
+
+  function doFailingApprove() {
+    token.safeApprove(0, 0);
+  }
+}