Add and test function to invalidate nonce

src/UniStaker.sol

@@ -613,6 +613,12 @@ contract UniStaker is INotifiableRewardReceiver, Multicall, EIP712, Nonces {
       );
   }
 
+  /// @notice Allows an address to increment their nonce and therefore invalidate any pending signed
+  /// actions.
+  function invalidateNonce() external {
+    _useNonce(msg.sender);
+  }
+
   /// @notice Internal method which finds the existing surrogate contract—or deploys a new one if
   /// none exists—for a given delegatee.
   /// @param _delegatee Account for which a surrogate is sought.

test/UniStaker.t.sol

@@ -2648,6 +2648,49 @@ contract SetAdmin is UniStakerTest {
   }
 }
 
+contract InvalidateNonce is UniStakerTest {
+  using stdStorage for StdStorage;
+
+  function testFuzz_SucessfullyIncrementsTheNonceOfTheSender(address _caller, uint256 _initialNonce)
+    public
+  {
+    vm.assume(_caller != address(0));
+    vm.assume(_initialNonce != type(uint256).max);
+
+    stdstore.target(address(uniStaker)).sig("nonces(address)").with_key(_caller).checked_write(
+      _initialNonce
+    );
+
+    vm.prank(_caller);
+    uniStaker.invalidateNonce();
+
+    uint256 currentNonce = uniStaker.nonces(_caller);
+
+    assertEq(currentNonce, _initialNonce + 1, "Current nonce is incorrect");
+  }
+
+  function testFuzz_IncreasesTheNonceByTwoWhenCalledTwice(address _caller, uint256 _initialNonce)
+    public
+  {
+    vm.assume(_caller != address(0));
+    _initialNonce = bound(_initialNonce, 0, type(uint256).max - 2);
+
+    stdstore.target(address(uniStaker)).sig("nonces(address)").with_key(_caller).checked_write(
+      _initialNonce
+    );
+
+    vm.prank(_caller);
+    uniStaker.invalidateNonce();
+
+    vm.prank(_caller);
+    uniStaker.invalidateNonce();
+
+    uint256 currentNonce = uniStaker.nonces(_caller);
+
+    assertEq(currentNonce, _initialNonce + 2, "Current nonce is incorrect");
+  }
+}
+
 contract UniStakerRewardsTest is UniStakerTest {
   // Helper methods for dumping contract state related to rewards calculation for debugging
   function __dumpDebugGlobalRewards() public view {