Add unclaimed reward invariant test (#80)

test/Staker.invariants.t.sol

@@ -77,6 +77,15 @@ contract StakerInvariants is Test {
     );
   }
 
+  function invariant_Sum_of_unclaimed_reward_should_be_less_than_or_equal_to_total_rewards_balance()
+    public
+  {
+    assertLe(
+      handler.reduceDeposits(0, this.accumulateUnclaimedReward),
+      rewardToken.balanceOf(address(govStaker))
+    );
+  }
+
   function invariant_RewardPerTokenAccumulatedCheckpoint_should_be_greater_or_equal_to_the_last_rewardPerTokenAccumulatedCheckpoint(
   ) public view {
     assertGe(
@@ -96,6 +105,13 @@ contract StakerInvariants is Test {
     return balance + govStaker.depositorTotalStaked(depositor);
   }
 
+  function accumulateUnclaimedReward(
+    uint256 unclaimedReward,
+    StakerHarness.DepositIdentifier depositId
+  ) external view returns (uint256) {
+    return unclaimedReward + govStaker.unclaimedReward(depositId);
+  }
+
   function accumulateSurrogateBalance(uint256 balance, address delegate)
     external
     view

test/helpers/DepositIdSet.sol

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+pragma solidity ^0.8.23;
+
+import {Staker} from "src/Staker.sol";
+
+struct DepositIdSet {
+  Staker.DepositIdentifier[] ids;
+  mapping(Staker.DepositIdentifier => bool) saved;
+}
+
+library LibDepositIdSet {
+  function reduce(
+    DepositIdSet storage s,
+    uint256 acc,
+    function(uint256,Staker.DepositIdentifier) external returns (uint256) func
+  ) internal returns (uint256) {
+    for (uint256 i; i < s.ids.length; ++i) {
+      acc = func(acc, s.ids[i]);
+    }
+    return acc;
+  }
+
+  function add(DepositIdSet storage s, Staker.DepositIdentifier id) internal {
+    if (!s.saved[id]) {
+      s.ids.push(id);
+      s.saved[id] = true;
+    }
+  }
+}

test/helpers/Staker.handler.sol

@@ -6,11 +6,13 @@ import {StdCheats} from "forge-std/StdCheats.sol";
 import {StdUtils} from "forge-std/StdUtils.sol";
 import {console} from "forge-std/console.sol";
 import {AddressSet, LibAddressSet} from "../helpers/AddressSet.sol";
+import {DepositIdSet, LibDepositIdSet} from "../helpers/DepositIdSet.sol";
 import {Staker} from "src/Staker.sol";
 import {IERC20} from "openzeppelin/token/ERC20/IERC20.sol";
 
 contract StakerHandler is CommonBase, StdCheats, StdUtils {
   using LibAddressSet for AddressSet;
+  using LibDepositIdSet for DepositIdSet;
 
   // system setup
   Staker public govStaker;
@@ -23,6 +25,7 @@ contract StakerHandler is CommonBase, StdCheats, StdUtils {
   AddressSet internal _depositors;
   AddressSet internal _delegates;
   AddressSet internal _claimers;
+  DepositIdSet internal _depositIdSet;
   AddressSet internal _surrogates;
   AddressSet internal _rewardNotifiers;
   mapping(address => uint256[]) internal _depositIds;
@@ -113,6 +116,7 @@ contract StakerHandler is CommonBase, StdCheats, StdUtils {
 
     // update handler state
     _depositIds[_currentActor].push(ghost_depositCount);
+    _depositIdSet.add(Staker.DepositIdentifier.wrap(ghost_depositCount));
     ghost_depositCount++;
     _surrogates.add(address(govStaker.surrogates(_delegatee)));
     ghost_stakeSum += _amount;
@@ -207,6 +211,13 @@ contract StakerHandler is CommonBase, StdCheats, StdUtils {
     return _claimers.reduce(acc, func);
   }
 
+  function reduceDeposits(
+    uint256 acc,
+    function(uint256,Staker.DepositIdentifier) external returns (uint256) func
+  ) public returns (uint256) {
+    return _depositIdSet.reduce(acc, func);
+  }
+
   function reduceDelegates(uint256 acc, function(uint256,address) external returns (uint256) func)
     public
     returns (uint256)