Added a shuffle test with negative hash codes for some keys (this was a bug earlier)

src/test/spark/ShuffleSuite.scala

@@ -31,6 +31,17 @@ class ShuffleSuite extends FunSuite {
     assert(valuesFor2.toList.sorted === List(1))
   }
 
+  test("groupByKey with negative key hash codes") {
+    val sc = new SparkContext("local", "test")
+    val pairs = sc.parallelize(Array((-1, 1), (-1, 2), (-1, 3), (2, 1)))
+    val groups = pairs.groupByKey().collect()
+    assert(groups.size === 2)
+    val valuesForMinus1 = groups.find(_._1 == -1).get._2
+    assert(valuesForMinus1.toList.sorted === List(1, 2, 3))
+    val valuesFor2 = groups.find(_._1 == 2).get._2
+    assert(valuesFor2.toList.sorted === List(1))
+  }
+
   test("groupByKey with many output partitions") {
     val sc = new SparkContext("local", "test")
     val pairs = sc.parallelize(Array((1, 1), (1, 2), (1, 3), (2, 1)))