create new test cases for takeSample from an empty red

Author: CodingCat

core/src/test/scala/org/apache/spark/rdd/RDDSuite.scala

@@ -457,10 +457,7 @@ class RDDSuite extends FunSuite with SharedSparkContext {
 
   test("takeSample") {
     val data = sc.parallelize(1 to 100, 2)
-    val emptySet = data.mapPartitions { iter => Iterator.empty }
 
-    val sample = emptySet.takeSample(false, 20, 1)
-    assert(sample.length === 0)
     for (seed <- 1 to 5) {
       val sample = data.takeSample(withReplacement=false, 20, seed)
       assert(sample.size === 20)        // Got exactly 20 elements
@@ -492,6 +489,12 @@ class RDDSuite extends FunSuite with SharedSparkContext {
     }
   }
 
+  test("takeSample from an empty rdd") {
+    val emptySet = sc.parallelize(Seq.empty[Int], 2)
+    val sample = emptySet.takeSample(false, 20, 1)
+    assert(sample.length === 0)
+  }
+
   test("randomSplit") {
     val n = 600
     val data = sc.parallelize(1 to n, 2)