Merge pull request #772 from 0xProject/add-coverage-instructions

Improve Contracts README Testing Section

packages/contracts/README.md

@@ -64,11 +64,51 @@ yarn lint
 yarn test
 ```
 
-### Run Tests Against Geth
+#### Testing options
 
-Follow the instructions in the README for the devnet package to start the
-devnet.
+###### Revert stack traces
+
+If you want to see helpful stack traces (incl. line number, code snippet) for smart contract reverts, run the tests with:
+
+```
+yarn test:trace
+```
+
+**Note:** This currently slows down the test runs and is therefore not enabled by default.
+
+###### Backing Ethereum node
+
+By default, our tests run against an in-process [Ganache](https://github.com/trufflesuite/ganache-core) instance. In order to run the tests against [Geth](https://github.com/ethereum/go-ethereum), first follow the instructions in the README for the devnet package to start the devnet Geth node. Then run:
 
 ```bash
 TEST_PROVIDER=geth yarn test
 ```
+
+###### Code coverage
+
+In order to see the Solidity code coverage output generated by `@0xproject/sol-cov`, run:
+
+```
+yarn test:coverage
+```
+
+###### Gas profiler
+
+In order to profile the gas costs for a specific smart contract call/transaction, you can run the tests in `profiler` mode.
+
+**Note:** Traces emitted by ganache have incorrect gas costs so we recommend using Geth for profiling.
+
+```
+TEST_PROVIDER=geth yarn test:profiler
+```
+
+You'll see a warning that you need to explicitly enable and disable the profiler before and after the block of code you want to profile.
+
+```typescript
+import { profiler } from './utils/profiler';
+profiler.start();
+// Some call to a smart contract
+profiler.stop();
+```
+
+Without explicitly starting and stopping the profiler, the profiler output will be too busy, and therefore unusable.