add additional check: reward caller is already set

Author: SidestreamSweatyPumpkin

contracts/bonding/BondingManager.sol

@@ -211,6 +211,7 @@ contract BondingManager is ManagerProxyTarget, IBondingManager {
      */
     function confirmRewardCaller(address _rewardCaller) external whenSystemNotPaused {
         require(rewardCallerToTranscoderProposed[_rewardCaller] == msg.sender, "reward caller was not proposed");
+        require(rewardCallerToTranscoderConfirmed[_rewardCaller] == address(0), "reward caller is already set");
         rewardCallerToTranscoderProposed[_rewardCaller] = address(0);
         rewardCallerToTranscoderConfirmed[_rewardCaller] = msg.sender;
         emit RewardCallerConfirmed(msg.sender, _rewardCaller);
@@ -222,7 +223,7 @@ contract BondingManager is ManagerProxyTarget, IBondingManager {
      * @dev Only callable by the transcoder, when the _rewardCaller was already proposed
      */
     function removeRewardCaller(address _rewardCaller) external whenSystemNotPaused {
-        require(rewardCallerToTranscoderConfirmed[_rewardCaller] == msg.sender, "only relevant transcoder can unset");
+        require(rewardCallerToTranscoderConfirmed[_rewardCaller] == msg.sender, "only relevant transcoder can remove");
         rewardCallerToTranscoderConfirmed[_rewardCaller] = address(0);
         emit RewardCallerRemoved(msg.sender, _rewardCaller);
     }

test/unit/BondingManager.js

@@ -5414,12 +5414,14 @@ describe("BondingManager", () => {
 
     describe("reward", () => {
         let transcoder
+        let transcoder2
         let nonTranscoder
         let currentRound
 
         beforeEach(async () => {
             transcoder = signers[0]
-            nonTranscoder = signers[1]
+            transcoder2 = signers[1]
+            nonTranscoder = signers[2]
             currentRound = 100
 
             await fixture.roundsManager.setMockBool(
@@ -6208,7 +6210,26 @@ describe("BondingManager", () => {
                     .connect(nonTranscoder)
                     .removeRewardCaller(nonTranscoder.address)
                 await expect(removeRewardCallerTx).to.be.revertedWith(
-                    "only relevant transcoder can unset"
+                    "only relevant transcoder can remove"
+                )
+            })
+
+            it("impossible to confirm RewardCaller for a second transcoder", async () => {
+                await bondingManager
+                    .connect(nonTranscoder)
+                    .proposeTranscoderForRewardCaller(transcoder.address)
+                await bondingManager
+                    .connect(transcoder)
+                    .confirmRewardCaller(nonTranscoder.address)
+                await bondingManager
+                    .connect(nonTranscoder)
+                    .proposeTranscoderForRewardCaller(transcoder2.address)
+
+                const removeRewardCallerTx = bondingManager
+                    .connect(transcoder2)
+                    .confirmRewardCaller(nonTranscoder.address)
+                await expect(removeRewardCallerTx).to.be.revertedWith(
+                    "reward caller is already set"
                 )
             })