* Fixed typo in tree suite test "do not choose split that does not satisfy min instance per node requirements"

* small style fixes

Author: jkbradley

mllib/src/main/scala/org/apache/spark/mllib/tree/DecisionTree.scala

@@ -929,7 +929,7 @@ object DecisionTree extends Serializable with Logging {
       }
     }.maxBy(_._2.gain)
 
-    require(predict.isDefined, "must calculate predict for each node")
+    assert(predict.isDefined, "must calculate predict for each node")
 
     (bestSplit, bestSplitStats, predict.get)
   }

mllib/src/main/scala/org/apache/spark/mllib/tree/model/Predict.scala

@@ -17,18 +17,14 @@
 
 package org.apache.spark.mllib.tree.model
 
-import org.apache.spark.annotation.DeveloperApi
-
 /**
- * :: DeveloperApi ::
  * Predicted value for a node
  * @param predict predicted value
  * @param prob probability of the label (classification only)
  */
-@DeveloperApi
 private[tree] class Predict(
     val predict: Double,
-    val prob: Double = 0.0) extends Serializable{
+    val prob: Double = 0.0) extends Serializable {
 
   override def toString = {
     "predict = %f, prob = %f".format(predict, prob)

mllib/src/test/scala/org/apache/spark/mllib/tree/DecisionTreeSuite.scala

@@ -706,8 +706,8 @@ class DecisionTreeSuite extends FunSuite with LocalSparkContext {
     assert(bestInfoStats == InformationGainStats.invalidInformationGainStats)
   }
 
-  test("don't choose split that doesn't satisfy min instance per node requirements") {
-    // if a split doesn't satisfy min instances per node requirements,
+  test("do not choose split that does not satisfy min instance per node requirements") {
+    // if a split does not satisfy min instances per node requirements,
     // this split is invalid, even though the information gain of split is large.
     val arr = new Array[LabeledPoint](4)
     arr(0) = new LabeledPoint(0.0, Vectors.dense(0.0, 1.0))
@@ -727,7 +727,7 @@ class DecisionTreeSuite extends FunSuite with LocalSparkContext {
 
     assert(bestSplits.length == 1)
     val bestSplit = bestSplits(0)._1
-    val bestSplitStats = bestSplits(0)._1
+    val bestSplitStats = bestSplits(0)._2
     assert(bestSplit.feature == 1)
     assert(bestSplitStats != InformationGainStats.invalidInformationGainStats)
   }