Add Echidna fuzzing with CI support

.github/workflows/echidna.yml

@@ -0,0 +1,50 @@
+name: Echidna Test
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        test:
+          - Echidna_Deposit_Withdraw
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/setup-node@v2
+      with:
+        node-version: '16'
+        cache: 'yarn'
+    - uses: actions/setup-python@v2
+      with:
+        python-version: '3.x'
+
+    - run: yarn install
+    - run: yarn run hardhat compile
+
+    - name: Cache ${{ matrix.test }} corpus
+      uses: actions/cache@v2
+      with:
+        path: corpus
+        key: abi-${{ matrix.test }}-v2
+
+    - name: Run Echidna
+      uses: crytic/echidna-action@v1
+      with:
+        solc-version: 0.8.10
+        files: .
+        contract: ${{ matrix.test }}
+        crytic-args: --hardhat-ignore-compile
+        config: contracts/echidna/${{ matrix.test }}.yml
+
+    - name: Upload ${{ matrix.test }} coverage
+      uses: actions/upload-artifact@v2
+      with:
+        name: coverage-${{ matrix.test }}
+        path: corpus/covered.*

.gitignore

@@ -14,3 +14,5 @@ deployments/hardhat
 deployments/docker
 subgraph/generated
 subgraph/tests/.bin/*
+crytic-export/
+corpus/

contracts/echidna/Addresses.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity =0.8.10;
+
+import "../Vault.sol";
+import "../test/TestERC20.sol";
+
+contract Addresses {
+    Vault vault = Vault(0x6A4A62E5A7eD13c361b176A5F62C2eE620Ac0DF8);
+    TestERC20 underlying = TestERC20(0x1dC4c1cEFEF38a777b15aA20260a54E584b16C48);
+}

contracts/echidna/Echidna_Deposit_Withdraw.sol

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity =0.8.10;
+import "./Helper.sol";
+
+contract Echidna_Deposit_Withdraw is Helper {
+
+    // zero address should always revert
+    function withdraw_zero_address_recipient(uint256[] memory _ids) public {
+        withdraw_should_revert(address(0), _ids);
+    }
+
+    function withdraw_should_revert(address recipient, uint256[] memory _ids) internal {
+        try vault.withdraw(recipient, _ids) {
+            assert(false);
+        } catch {
+            assert(true);
+        }
+    }
+}

contracts/echidna/Echidna_Deposit_Withdraw.yml

@@ -0,0 +1,6 @@
+initialize: contracts/echidna/init.json
+coverage: true
+testMode: assertion
+testLimit: 30000
+corpusDir: 'corpus'
+codeSize: 0xfffffffffff

contracts/echidna/Helper.sol

@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity =0.8.10;
+import "./Addresses.sol";
+
+contract Helper is Addresses {
+
+
+}