Add address 0 check to isContract

Add tests.

test/TestDelegateProxy.sol

@@ -68,6 +68,17 @@ contract TestDelegateProxy is DelegateProxy {
         delegatedFwd(target, target.fail.selector.toBytes());
     }
 
+    function testIsContractZero() {
+        bool result = isContract(address(0));
+        Assert.isFalse(result, "should return false");
+    }
+
+    function testIsContractAddress() {
+        address nonContract = 0x1234;
+        bool result = isContract(nonContract);
+        Assert.isFalse(result, "should return false");
+    }
+
     // keep as last test as it will kill this contract
     function testDieIfMinReturn0() {
         delegatedFwd(target, target.die.selector.toBytes());

test/evm_script.js

@@ -336,4 +336,20 @@ contract('EVM Script', accounts => {
             })
         })
     })
+
+    context('isContract tests', async () => {
+        let delegateScript
+
+        before(async () => {
+            delegateScript = await getContract('DelegateScriptWrapper').new()
+        })
+
+        it('fails if address is 0', async () => {
+            assert.isFalse(await delegateScript.isContractWrapper('0x0'), "should return false")
+        })
+
+        it('fails if dst is not a contract', async () => {
+            assert.isFalse(await delegateScript.isContractWrapper('0x1234'), "should return false")
+        })
+    })
 })

test/mocks/DelegateScriptWrapper.sol

@@ -0,0 +1,10 @@
+pragma solidity 0.4.18;
+
+import "../../contracts/evmscript/executors/DelegateScript.sol";
+
+
+contract DelegateScriptWrapper is DelegateScript {
+    function isContractWrapper(address _target) public view returns (bool) {
+        return isContract(_target);
+    }
+}