spec: fix partioning logic for odd number of files

If there are an odd number of files to split, the last file would go into a bucket outside of the valid range. Fix this by using Math.ceil() instead of Math.floor()

flag = none

Change-Id: I51b8e8f66a87c8cd725441a4b10e9a77426223e4
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/242785
Reviewed-by: James Butters <jbutters@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
QA-Review: Aaron Ogata <aogata@instructure.com>
Product-Review: Aaron Ogata <aogata@instructure.com>

webpack.test.config.js

@@ -18,6 +18,7 @@
 
 process.env.NODE_ENV = 'test'
 
+const assert = require('assert')
 const fs = require('fs')
 const path = require('path')
 const webpack = require('webpack')
@@ -81,13 +82,15 @@ const isPartitionMatch = (resource, partitions, partitionIndex) => {
 const makeSortedPartitions = (arr, partitionCount) => {
   const sortedArr = arr.sort()
   const sortedArrLength = sortedArr.length
-  const chunkSize = Math.floor(sortedArrLength / partitionCount)
+  const chunkSize = Math.ceil(sortedArrLength / partitionCount)
   const R = []
 
   for (let i = 0; i < sortedArrLength; i += chunkSize) {
     R.push(sortedArr.slice(i, i + chunkSize))
   }
 
+  assert(R.length <= partitionCount)
+
   return R
 }