first pass (#71)

packages/contracts/contracts/test-helpers/Helper_GasMeasurer.sol

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract Helper_GasMeasurer {
+    function measureCallGas(
+        address _target,
+        bytes memory _data
+    )
+        public
+        returns ( uint )
+    {
+        uint gasBefore;
+        uint gasAfter;
+
+        uint calldataStart;
+        uint calldataLength;
+        assembly {
+            calldataStart := add(_data,0x20)
+            calldataLength := mload(_data)
+        }
+
+        bool success;
+        assembly {
+            gasBefore := gas()
+            success := call(gas(), _target, 0, calldataStart, calldataLength, 0, 0)
+            gasAfter := gas()
+        }
+        require(success, "Call failed, but calls we want to measure gas for should succeed!");
+
+        return gasBefore - gasAfter;
+    }
+}

packages/contracts/package.json

@@ -19,9 +19,9 @@
     "build:typechain": "buidler typechain",
     "test": "yarn run test:contracts",
     "test:contracts": "buidler test --show-stack-traces",
+    "test:gas": "buidler test \"test/contracts/OVM/execution/OVM_StateManager.gas-spec.ts\" --no-compile --show-stack-traces",
     "lint": "yarn run lint:typescript",
     "lint:typescript": "tslint --format stylish --project .",
-    "lint:fix": "yarn run lint:fix:typescript",
     "lint:fix:typescript": "prettier --config prettier-config.json --write \"buidler.config.ts\" \"{src,test}/**/*.ts\"",
     "clean": "rm -rf ./artifacts ./build ./cache",
     "deploy": "./bin/deploy.js"