test: add test for max key limit

Author: blockgroot

test/foundry_tests/PermissionlessNodeRegistry.t.sol

@@ -256,6 +256,21 @@ contract PermissionlessNodeRegistryTest is Test {
         assertEq(nodeRegistry.isExistingPubkey(pubkeys[0]), true);
     }
 
+    function test_addValidatorKeysWithLLimitExceed() public {
+        (
+            bytes[] memory pubkeys,
+            bytes[] memory preDepositSignature,
+            bytes[] memory depositSignature
+        ) = getValidatorKeys();
+        vm.prank(staderManager);
+        nodeRegistry.updateMaxKeyPerOperator(2); // Limit is 2 and trying to add 3 keys
+        startHoax(address(this));
+        nodeRegistry.onboardNodeOperator(true, "testOP", payable(address(this)));
+        vm.expectRevert(IPermissionlessNodeRegistry.MaxKeyLimitExceed.selector);
+        nodeRegistry.addValidatorKeys{ value: 12 ether }(pubkeys, preDepositSignature, depositSignature);
+        vm.stopPrank();
+    }
+
     function testAddValidatorKeysNotEnoughSDCollateral() public {
         (
             bytes[] memory pubkeys,