get challenge id

contracts/Challenge.sol

@@ -55,6 +55,7 @@ contract Challenge {
   // create challenge
   uint256 public lastChallengeId = 0;
 
+  event ChallengeCreate(uint256 challengeId);
   function newChallengeTrusted(bytes32 startState, bytes32 finalSystemState, uint256 stepCount) internal returns (uint256) {
     uint256 challengeId = lastChallengeId;
     Chal storage c = challenges[challengeId];
@@ -73,6 +74,7 @@ contract Challenge {
     c.R = stepCount;
 
     // find me later
+    emit ChallengeCreate(challengeId);
     return challengeId;
   }
 

test/challenge_test.js

@@ -30,7 +30,7 @@ describe("Challenge contract", function () {
     let preimages = Object.assign({}, startTrie['preimages'], finalTrie['preimages']);
     const finalSystemState = finalTrie['root']
 
-    let args = [blockNumberN, blockNp1Rlp, assertionRoot, finalSystemState, 1]
+    let args = [blockNumberN, blockNp1Rlp, assertionRoot, finalSystemState, finalTrie['step']]
     let cdat = c.interface.encodeFunctionData("InitiateChallenge", args)
     let nodes = await getTrieNodesForCall(c, cdat, preimages)
 
@@ -39,6 +39,9 @@ describe("Challenge contract", function () {
       await mm.AddTrieNode(n)
     }
     let ret = await c.InitiateChallenge(...args)
-    console.log(await ret.wait())
+    let receipt = await ret.wait()
+    // ChallengeCreate event
+    let challengeId = receipt.events[0].args['challengeId'].toNumber()
+    console.log("new challenge with id", challengeId)
   }).timeout(60000)
 })
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