Fix flaky tests

By ensuring that there's enough blocks left
for submitting a proof.

contracts/Proofs.sol

@@ -75,6 +75,10 @@ contract Proofs {
     return uint8(pointer);
   }
 
+  function _getPointer(bytes32 id) internal view returns (uint8) {
+    return _getPointer(id, currentPeriod());
+  }
+
   function _getChallenge(uint8 pointer) internal view returns (bytes32) {
     bytes32 hash = blockhash(block.number - 1 - pointer);
     assert(uint256(hash) != 0);

contracts/Storage.sol

@@ -68,6 +68,10 @@ contract Storage is Collateral, Marketplace, Proofs {
     return _getChallenge(contractId);
   }
 
+  function getPointer(bytes32 id) public view returns (uint8) {
+    return _getPointer(id);
+  }
+
   function submitProof(bytes32 contractId, bool proof) public {
     _submitProof(contractId, proof);
   }

contracts/TestProofs.sol

@@ -48,6 +48,10 @@ contract TestProofs is Proofs {
     return _getChallenge(id);
   }
 
+  function getPointer(bytes32 id) public view returns (uint8) {
+    return _getPointer(id);
+  }
+
   function submitProof(bytes32 id, bool proof) public {
     _submitProof(id, proof);
   }

test/Proofs.test.js

@@ -107,7 +107,12 @@ describe("Proofs", function () {
 
     async function waitUntilProofIsRequired(id) {
       await advanceTimeTo(periodEnd(periodOf(await currentTime())))
-      while (!(await proofs.isProofRequired(id))) {
+      while (
+        !(
+          (await proofs.isProofRequired(id)) &&
+          (await proofs.getPointer(id)) < 250
+        )
+      ) {
         await advanceTime(period)
       }
     }