[SPARK-7854] [TEST] refine Kryo test suite

this modification is according to JoshRosen 's comments, for details, please refer to [#5934](https://github.com/apache/spark/pull/5934/files#r30949751).

Author: Zhang, Liye <liye.zhang@intel.com>

Closes #6395 from liyezhang556520/kryoTest and squashes the following commits:

da214c8 [Zhang, Liye] refine Kryo test suite accroding to Josh's comments

core/src/test/scala/org/apache/spark/serializer/KryoSerializerSuite.scala

@@ -34,38 +34,41 @@ class KryoSerializerSuite extends FunSuite with SharedSparkContext {
   conf.set("spark.serializer", "org.apache.spark.serializer.KryoSerializer")
   conf.set("spark.kryo.registrator", classOf[MyRegistrator].getName)
 
-  test("configuration limits") {
-    val conf1 = conf.clone()
+  test("SPARK-7392 configuration limits") {
     val kryoBufferProperty = "spark.kryoserializer.buffer"
     val kryoBufferMaxProperty = "spark.kryoserializer.buffer.max"
-    conf1.set(kryoBufferProperty, "64k")
-    conf1.set(kryoBufferMaxProperty, "64m")
-    new KryoSerializer(conf1).newInstance()
+    
+    def newKryoInstance(
+        conf: SparkConf,
+        bufferSize: String = "64k",
+        maxBufferSize: String = "64m"): SerializerInstance = {
+      val kryoConf = conf.clone()
+      kryoConf.set(kryoBufferProperty, bufferSize)
+      kryoConf.set(kryoBufferMaxProperty, maxBufferSize)
+      new KryoSerializer(kryoConf).newInstance()
+    }
+    
+    // test default values
+    newKryoInstance(conf, "64k", "64m")
     // 2048m = 2097152k
-    conf1.set(kryoBufferProperty, "2097151k")
-    conf1.set(kryoBufferMaxProperty, "64m")
     // should not throw exception when kryoBufferMaxProperty < kryoBufferProperty
-    new KryoSerializer(conf1).newInstance()
-    conf1.set(kryoBufferMaxProperty, "2097151k")
-    new KryoSerializer(conf1).newInstance()
-    val conf2 = conf.clone()
-    conf2.set(kryoBufferProperty, "2048m")
-    val thrown1 = intercept[IllegalArgumentException](new KryoSerializer(conf2).newInstance())
+    newKryoInstance(conf, "2097151k", "64m")
+    // test maximum size with unit of KiB
+    newKryoInstance(conf, "2097151k", "2097151k")
+    // should throw exception with bufferSize out of bound
+    val thrown1 = intercept[IllegalArgumentException](newKryoInstance(conf, "2048m"))
     assert(thrown1.getMessage.contains(kryoBufferProperty))
-    val conf3 = conf.clone()
-    conf3.set(kryoBufferMaxProperty, "2048m")
-    val thrown2 = intercept[IllegalArgumentException](new KryoSerializer(conf3).newInstance())
+    // should throw exception with maxBufferSize out of bound
+    val thrown2 = intercept[IllegalArgumentException](
+        newKryoInstance(conf, maxBufferSize = "2048m"))
     assert(thrown2.getMessage.contains(kryoBufferMaxProperty))
-    val conf4 = conf.clone()
-    conf4.set(kryoBufferProperty, "2g")
-    conf4.set(kryoBufferMaxProperty, "3g")
-    val thrown3 = intercept[IllegalArgumentException](new KryoSerializer(conf4).newInstance())
+    // should throw exception when both bufferSize and maxBufferSize out of bound
+    // exception should only contain "spark.kryoserializer.buffer"
+    val thrown3 = intercept[IllegalArgumentException](newKryoInstance(conf, "2g", "3g"))
     assert(thrown3.getMessage.contains(kryoBufferProperty))
     assert(!thrown3.getMessage.contains(kryoBufferMaxProperty))
-    val conf5 = conf.clone()
-    conf5.set(kryoBufferProperty, "8m")
-    conf5.set(kryoBufferMaxProperty, "9m")
-    new KryoSerializer(conf5).newInstance()
+    // test configuration with mb is supported properly
+    newKryoInstance(conf, "8m", "9m")
   }
   
   test("basic types") {