++ setter for oracle address

packages/protocol/contracts-0.8/common/EpochManager.sol

@@ -57,6 +57,7 @@ contract EpochManager is
 
   uint256 public firstKnownEpoch;
   uint256 private currentEpochNumber;
+  address public oracleAddress;
   address[] public elected;
 
   mapping(address => ProcessedGroup) public processedGroups;
@@ -77,6 +78,7 @@ contract EpochManager is
    */
   event EpochProcessingEnded(uint256 indexed epochNumber);
   event EpochDurationSet(uint256 indexed newEpochDuration);
+  event OracleAddressSet(address indexed newOracleAddress);
 
   /**
    * @notice Emitted when an epoch payment is sent.
@@ -121,6 +123,7 @@ contract EpochManager is
     _transferOwnership(msg.sender);
     setRegistry(registryAddress);
     setEpochDuration(newEpochDuration);
+    setOracleAddress(registry.getAddressForOrDie(SORTED_ORACLES_REGISTRY_ID));
   }
 
   // DESIGNDESICION(XXX): we assume that the first epoch on the L2 starts as soon as the system is initialized
@@ -368,11 +371,25 @@ contract EpochManager is
    * @dev Can only be set by owner.
    */
   function setEpochDuration(uint256 newEpochDuration) public onlyOwner {
+    require(newEpochDuration > 0, "New epoch duration must be greater than zero.");
     require(!isOnEpochProcess(), "Cannot change epoch duration during processing.");
     epochDuration = newEpochDuration;
     emit EpochDurationSet(newEpochDuration);
   }
 
+  /**
+   * @notice Sets the address of the Oracle used by this contract.
+   * @param newOracleAddress The address of the new oracle.
+   * @dev Can only be set by owner.
+   */
+  function setOracleAddress(address newOracleAddress) public onlyOwner {
+    require(newOracleAddress != address(0), "Cannot set address zero as the Oracle.");
+    require(newOracleAddress != oracleAddress, "Oracle address cannot be the same.");
+    require(!isOnEpochProcess(), "Cannot change oracle address during epoch processing.");
+    oracleAddress = newOracleAddress;
+    emit OracleAddressSet(newOracleAddress);
+  }
+
   function isTimeForNextEpoch() public view returns (bool) {
     return block.timestamp >= epochs[currentEpochNumber].startTimestamp + epochDuration;
   }
@@ -409,9 +426,8 @@ contract EpochManager is
 
     // Mint all cUSD required for payment and the corresponding CELO
     validators.mintStableToEpochManager(totalRewards);
-    // this should have a setter for the oracle.
 
-    (uint256 numerator, uint256 denominator) = IOracle(address(getSortedOracles())).getExchangeRate(
+    (uint256 numerator, uint256 denominator) = IOracle(oracleAddress).getExchangeRate(
       address(getStableToken())
     );
 

packages/protocol/test-sol/unit/common/EpochManager.t.sol

@@ -63,6 +63,7 @@ contract EpochManagerTest is Test, TestConstants, Utils08 {
 
   event EpochProcessingStarted(uint256 indexed epochNumber);
   event EpochDurationSet(uint256 indexed newEpochDuration);
+  event OracleAddressSet(address indexed newOracleAddress);
 
   function setUp() public virtual {
     epochManager = new EpochManager_WithMocks();
@@ -132,6 +133,7 @@ contract EpochManagerTest_initialize is EpochManagerTest {
   function test_initialize() public virtual {
     assertEq(address(epochManager.registry()), REGISTRY_ADDRESS);
     assertEq(epochManager.epochDuration(), 10);
+    assertEq(epochManager.oracleAddress(), address(sortedOracles));
   }
 
   function test_Reverts_WhenAlreadyInitialized() public virtual {
@@ -246,6 +248,7 @@ contract EpochManagerTest_startNextEpochProcess is EpochManagerTest {
     assertEq(reserveBalanceAfter, reserveBalanceBefore + 4);
   }
 }
+
 contract EpochManagerTest_setEpochDuration is EpochManagerTest {
   uint256 newEpochDuration = 5 * DAY;
 
@@ -269,6 +272,52 @@ contract EpochManagerTest_setEpochDuration is EpochManagerTest {
     vm.expectRevert("Cannot change epoch duration during processing.");
     epochManager.setEpochDuration(newEpochDuration);
   }
+
+  function test_Reverts_WhenNewEpochDurationIsZero() public {
+    initializeEpochManagerSystem();
+
+    vm.expectRevert("New epoch duration must be greater than zero.");
+    epochManager.setEpochDuration(0);
+  }
+}
+
+contract EpochManagerTest_setOracleAddress is EpochManagerTest {
+  address newOracleAddress = actor("newOarcle");
+
+  function test_setsNewOracleAddress() public {
+    initializeEpochManagerSystem();
+    epochManager.setOracleAddress(newOracleAddress);
+    assertEq(epochManager.oracleAddress(), newOracleAddress);
+  }
+
+  function test_Emits_OracleAddressSetEvent() public {
+    initializeEpochManagerSystem();
+
+    vm.expectEmit(true, true, true, true);
+    emit OracleAddressSet(newOracleAddress);
+    epochManager.setOracleAddress(newOracleAddress);
+  }
+
+  function test_Reverts_WhenIsOnEpochProcess() public {
+    initializeEpochManagerSystem();
+    epochManager.startNextEpochProcess();
+    vm.expectRevert("Cannot change oracle address during epoch processing.");
+    epochManager.setOracleAddress(newOracleAddress);
+  }
+
+  function test_Reverts_WhenNewOracleAddressIsZero() public {
+    initializeEpochManagerSystem();
+
+    vm.expectRevert("Cannot set address zero as the Oracle.");
+    epochManager.setOracleAddress(address(0));
+  }
+
+  function test_Reverts_WhenNewOracleAddressIsunchanged() public {
+    initializeEpochManagerSystem();
+
+    vm.expectRevert("Oracle address cannot be the same.");
+    epochManager.setOracleAddress(address(sortedOracles));
+  }
 }
 
 contract EpochManagerTest_sendValidatorPayment is EpochManagerTest {

packages/protocol/test-sol/unit/common/EpochManagerEnabler.t.sol

@@ -31,6 +31,7 @@ contract EpochManagerEnablerTest is Test, TestConstants, Utils08 {
 
   address accountsAddress;
   address nonOwner;
+  address oracle;
 
   uint256 epochDuration = DAY;
   uint256 numberValidators = 100;
@@ -50,6 +51,7 @@ contract EpochManagerEnablerTest is Test, TestConstants, Utils08 {
     accountsAddress = actor("accountsAddress");
 
     nonOwner = actor("nonOwner");
+    oracle = actor("oracle");
 
     deployCodeTo("MockRegistry.sol", abi.encode(false), REGISTRY_ADDRESS);
     deployCodeTo("Accounts.sol", abi.encode(false), accountsAddress);
@@ -61,6 +63,7 @@ contract EpochManagerEnablerTest is Test, TestConstants, Utils08 {
     registry.setAddressFor(EpochManagerEnablerContract, address(epochManagerEnabler));
     registry.setAddressFor(AccountsContract, address(accounts));
     registry.setAddressFor(CeloTokenContract, address(celoToken));
+    registry.setAddressFor(SortedOraclesContract, oracle);
     registry.setAddressFor(CeloUnreleasedTreasuryContract, address(celoUnreleasedTreasury));
 
     celoToken.setTotalSupply(CELO_SUPPLY_CAP);