Add last seen event data (#22)

* add last seen event data

* change to updated and add test

Author: hexonaut

src/forwarders/DSROracleForwarderBase.sol

@@ -10,6 +10,8 @@ import { IPot }                       from '../interfaces/IPot.sol';
  */
 abstract contract DSROracleForwarderBase {
 
+    event LastSeenPotDataUpdated(IDSROracle.PotData potData);
+
     IPot               public immutable pot;
     address            public immutable l2Oracle;
 
@@ -27,6 +29,7 @@ abstract contract DSROracleForwarderBase {
             rho: uint40(pot.rho())
         });
         _lastSeenPotData = potData;
+        emit LastSeenPotDataUpdated(potData);
         return abi.encodeCall(
             IDSRAuthOracle.setPotData,
             (potData)

test/DSROracleXChainIntegrationBase.t.sol

@@ -20,6 +20,8 @@ interface IPotDripLike {
 
 abstract contract DSROracleXChainIntegrationBaseTest is Test {
 
+    event LastSeenPotDataUpdated(IDSROracle.PotData potData);
+
     using DomainHelpers for *;
 
     uint256 constant CURR_DSR = 1.000000001547125957863212448e27;
@@ -81,6 +83,12 @@ abstract contract DSROracleXChainIntegrationBaseTest is Test {
         assertEq(forwarder.getLastSeenChi(), 0);
         assertEq(forwarder.getLastSeenRho(), 0);
 
+        vm.expectEmit(address(forwarder));
+        emit LastSeenPotDataUpdated(IDSROracle.PotData({
+            dsr: uint96(CURR_DSR),
+            chi: uint120(CURR_CHI),
+            rho: uint40(CURR_RHO)
+        }));
         doRefresh();
 
         data = forwarder.getLastSeenPotData();