diff --git a/test/helpers/AddressSet.sol b/test/helpers/AddressSet.sol
index 83327a7..323ed2c 100644
--- a/test/helpers/AddressSet.sol
+++ b/test/helpers/AddressSet.sol
@@ -17,6 +17,20 @@ library LibAddressSet {
     }
   }
 
+  function remove(AddressSet storage s, address addr) internal {
+    if (s.saved[addr]) {
+      uint256 len = s.addrs.length;
+      for(uint256 i = 0; i < len; ++i) {
+        if(s.addrs[i] == addr) {
+          s.addrs[i] = s.addrs[len-1];
+          break;
+        }
+      }
+      s.addrs.pop();
+      s.saved[addr] = false;
+    }
+  }
+
   function contains(AddressSet storage s, address addr) internal view returns (bool) {
     return s.saved[addr];
   }
@@ -39,8 +53,8 @@ library LibAddressSet {
   function reduce(
     AddressSet storage s,
     uint256 acc,
-    function(uint256,address) external returns (uint256) func
-  ) internal returns (uint256) {
+    function(uint256,address) external view returns (uint256) func
+  ) internal view returns (uint256) {
     for (uint256 i; i < s.addrs.length; ++i) {
       acc = func(acc, s.addrs[i]);
     }
