Fixed PackedRecordPointerSuite test.

Author: JoshRosen

core/src/test/java/org/apache/spark/shuffle/sort/PackedRecordPointerSuite.java

@@ -54,7 +54,9 @@ public void heap() throws IOException {
 
   @Test
   public void offHeap() throws IOException {
-    final SparkConf conf = new SparkConf().set("spark.memory.offHeap.enabled", "true");
+    final SparkConf conf = new SparkConf()
+      .set("spark.memory.offHeap.enabled", "true")
+      .set("spark.memory.offHeap.size", "10000");
     final TaskMemoryManager memoryManager =
       new TaskMemoryManager(new TestMemoryManager(conf), 0);
     final MemoryBlock page0 = memoryManager.allocatePage(128, null);