epochs: reintroduce test to check if we stay on the same epoch after moving fwd one block without passing epoch length (#182)

Author: abarmat

contracts/EpochManager.sol

@@ -124,6 +124,14 @@ contract EpochManager is Governed {
         return lastLengthUpdateBlock.add(epochsSinceUpdate().mul(epochLength));
     }
 
+    /**
+     * @dev Return the number of blocks that passed since current epoch started
+     * @return Blocks that passed since start of epoch
+     */
+    function currentEpochBlockSinceStart() public view returns (uint256) {
+        return blockNum() - currentEpochBlock();
+    }
+
     /**
      * @dev Return the number of epoch that passed since another epoch
      * @param _epoch Epoch to use as since epoch value

test/epochs.test.js

@@ -68,6 +68,21 @@ contract('EpochManager', ([me, other, governor]) => {
         expect(await this.epochManager.blockNum()).to.be.bignumber.eq(currentBlock)
       })
 
+      it('should return same starting block if we stay on the same epoch', async function() {
+        // Move right to the start of a new epoch
+        const blocksSinceEpochStart = await this.epochManager.currentEpochBlockSinceStart()
+        const blocksToNextEpoch = this.epochLength.sub(blocksSinceEpochStart)
+        await time.advanceBlockTo((await this.epochManager.blockNum()).add(blocksToNextEpoch))
+
+        const currentEpochBlockBefore = await this.epochManager.currentEpochBlock()
+
+        // Advance block - will not jump to next epoch
+        await time.advanceBlock()
+
+        const currentEpochBlockAfter = await this.epochManager.currentEpochBlock()
+        expect(currentEpochBlockAfter).to.be.bignumber.equal(currentEpochBlockBefore)
+      })
+
       it('should return next starting block if we move to the next epoch', async function() {
         const currentEpochBlockBefore = await this.epochManager.currentEpochBlock()