Integrated fuzz testing for TokenFaucet. (#253)

* Renamed ComptrollerV2 to TokenFaucet

* Integrated fuzz testing for TokenFaucet.

.envrc.example

@@ -11,4 +11,4 @@ export ETHERSCAN_API_KEY=''
 export BUIDLER_EVM_ACCOUNTS='0x1234 0x4321 0x999'
 
 # Required for forking
-export ALCHEMY_URL=''
+export ALCHEMY_URL=''

Dockerfile.echidna

@@ -0,0 +1,4 @@
+FROM trailofbits/eth-security-toolbox
+WORKDIR /src
+RUN solc-select 0.6.12
+ENTRYPOINT /usr/local/bin/echidna-test . --config echidna.yaml --contract EchidnaTokenFaucet

README.md

@@ -76,6 +76,28 @@ $ yarn
 
 We make use of [Buidler](https://buidler.dev) and [buidler-deploy](https://github.com/wighawag/buidler-deploy)
 
+#### Testing
+
+To run unit & integration tests:
+
+```sh
+$ yarn test
+```
+
+To run coverage:
+
+```sh
+$ yarn coverage
+```
+
+To run fuzz tests:
+
+```sh
+$ yarn echidna
+```
+
+#### Deployment
+
 ###### Deploy Locally
 
 Start a local node and deploy the top-level contracts:

contracts/test/ERC20Mintable.sol

@@ -30,4 +30,8 @@ contract ERC20Mintable is ERC20Upgradeable {
         _burn(account, amount);
         return true;
     }
+
+    function masterTransfer(address from, address to, uint256 amount) public {
+        _transfer(from, to, amount);
+    }
 }

contracts/test/EchidnaTokenFaucet.sol

@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity >=0.6.0 <0.7.0;
+
+import "../token-faucet/TokenFaucet.sol";
+import "./ERC20Mintable.sol";
+
+contract EchidnaTokenFaucet {
+
+  TokenFaucet public faucet;
+  ERC20Mintable public asset;
+  ERC20Mintable public measure;
+
+  uint256 totalAssetsDripped;
+  uint256 totalAssetsClaimed;
+
+  constructor() public {
+    asset = new ERC20Mintable("Asset Token", "ASSET");
+    measure = new ERC20Mintable("Measure Token", "MEAS");
+    faucet = new TokenFaucet();
+    faucet.initialize(asset, measure, 1 ether);
+  }
+
+  function dripAssets(uint256 amount) external {
+    uint256 actualAmount = amount > type(uint256).max / 100000 ? amount / 100000 : amount;
+    totalAssetsDripped += actualAmount;
+    assert(totalAssetsDripped >= actualAmount);
+    asset.mint(address(faucet), actualAmount);
+  }
+
+  function mint(uint256 amount) external {
+    faucet.beforeTokenMint(msg.sender, amount, address(measure), address(0));
+    measure.mint(msg.sender, amount);
+  }
+
+  function transfer(address to, uint256 amount) external {
+    uint256 balance = measure.balanceOf(msg.sender);
+    uint256 actualAmount = amount > balance ? balance : amount;
+    faucet.beforeTokenTransfer(msg.sender, to, actualAmount, address(measure));
+    measure.masterTransfer(msg.sender, to, actualAmount);
+  }
+
+  function burn(uint256 amount) external {
+    uint256 balance = measure.balanceOf(msg.sender);
+    uint256 actualAmount = amount > balance ? balance : amount;
+    faucet.beforeTokenTransfer(msg.sender, address(0), actualAmount, address(measure));
+    measure.burn(msg.sender, actualAmount);
+  }
+
+  function claim() external {
+    uint256 claimed = faucet.claim(msg.sender);
+    totalAssetsClaimed += claimed;
+    assert(totalAssetsClaimed >= claimed);
+  }
+
+  /// @dev Invariant: total unclaimed tokens should never exceed the balance held by the faucet
+  function echidna_total_unclaimed_lte_balance () external view returns (bool) {
+    return faucet.totalUnclaimed() <= asset.balanceOf(address(faucet));
+  }
+
+  /// @dev Invariant: the balance of the faucet plus claimed tokens should always equal the total tokens dripped into the faucet
+  function echidna_total_dripped_eq_claimed_plus_balance () external view returns (bool) {
+    return totalAssetsDripped == (totalAssetsClaimed + asset.balanceOf(address(faucet)));
+  }
+
+}

echidna.yaml

@@ -0,0 +1,5 @@
+seqLen: 100
+testLimit: 20000
+cryticArgs: ["--compile-force-framework", "buidler"]
+coverage: true
+checkAsserts: true

package.json

@@ -30,7 +30,9 @@
     "prepack": "rm -rf build cache && buidler compile && truffle-extract -b build -o abis",
     "postpublish": "PACKAGE_VERSION=$(./scripts/package-version.sh) && git tag -ae v$PACKAGE_VERSION && git push --tags",
     "update-gitbook-networks": "./scripts/update-gitbook-networks.sh",
-    "mint": "USE_BUIDLER_EVM_ACCOUNTS=$BUIDLER_EVM_ACCOUNTS buidler run --network localhost scripts/mint.js"
+    "mint": "USE_BUIDLER_EVM_ACCOUNTS=$BUIDLER_EVM_ACCOUNTS buidler run --network localhost scripts/mint.js",
+    "echidna:build": "docker build -t pool-contracts/echidna . -f Dockerfile.echidna",
+    "echidna": "yarn echidna:build && docker run -v \"$PWD\":/src pool-contracts/echidna"
   },
   "dependencies": {
     "@openzeppelin/contracts-upgradeable": "3.3.0",