added setUp yield into a16z tests

tests/ERC4626a16z.t.sol

@@ -1,15 +1,20 @@
 // SPDX-License-Identifier: BUSL-1.1
 pragma solidity >=0.8.0 <0.9.0;
 
+// modified
 import 'erc4626-tests/ERC4626.test.sol';
 
 import {TransparentUpgradeableProxy} from 'solidity-utils/contracts/transparent-proxy/TransparentUpgradeableProxy.sol';
 
 import {StakeToken} from 'src/contracts/StakeToken.sol';
 import {IRewardsController} from 'src/contracts/interfaces/IRewardsController.sol';
 
-import {MockRewardsController} from './utils/mock/MockRewardsController.sol';
-import {MockERC20Permit} from './utils/mock/MockERC20Permit.sol';
+import {MockRewardsController} from '../utils/mock/MockRewardsController.sol';
+import {MockERC20Permit} from '../utils/mock/MockERC20Permit.sol';
+
+interface ISlashable {
+  function slash(address to, uint256 amount) external;
+}
 
 contract ERC4626StdTest is ERC4626Test {
   function setUp() public override {
@@ -19,21 +24,17 @@ contract ERC4626StdTest is ERC4626Test {
     StakeToken stakeTokenImpl = new StakeToken(IRewardsController(mockRewardsController));
 
     _vault_ = address(
-      StakeToken(
-        address(
-          new TransparentUpgradeableProxy(
-            address(stakeTokenImpl),
-            address(0x2000),
-            abi.encodeWithSelector(
-              StakeToken.initialize.selector,
-              address(_underlying_),
-              'Mock ERC4626',
-              'MERC4626',
-              address(0x3000),
-              15 days,
-              2 days
-            )
-          )
+      new TransparentUpgradeableProxy(
+        address(stakeTokenImpl),
+        address(0x2000),
+        abi.encodeWithSelector(
+          StakeToken.initialize.selector,
+          address(_underlying_),
+          'Mock ERC4626',
+          'MERC4626',
+          address(0x3000),
+          15 days,
+          2 days
         )
       )
     );
@@ -42,4 +43,37 @@ contract ERC4626StdTest is ERC4626Test {
     _vaultMayBeEmpty = false;
     _unlimitedAmount = false;
   }
+
+  function whoCanSlash() public pure returns (address) {
+    return address(0x3000);
+  }
+
+  function MIN_ASSETS_REMAINING() public view returns (uint256) {
+    return StakeToken(_vault_).MIN_ASSETS_REMAINING();
+  }
+
+  function setUpYield(Init memory init) public override {
+    if (init.yield >= 0) {
+      // there's no way for direct gain opportunity in stakeToken
+    } else {
+      uint256 totalShares;
+
+      for (uint i = 0; i < N; i++) {
+        totalShares += init.share[i];
+      }
+
+      vm.assume(init.yield > type(int).min);
+
+      uint loss = uint(-1 * init.yield);
+
+      vm.assume(loss + MIN_ASSETS_REMAINING() < totalShares); // avoid overflow in conversion
+
+      vm.startPrank(whoCanSlash());
+      try ISlashable(_vault_).slash(address(0xdead), loss) {} catch {
+        vm.assume(false);
+      }
+
+      vm.stopPrank();
+    }
+  }
 }