add tests for LocalIndexEncoder

mllib/src/main/scala/org/apache/spark/ml/recommendation/ALS.scala

@@ -789,7 +789,7 @@ private object ALS extends Logging {
    *
    * @param numBlocks number of blocks
    */
-  private class LocalIndexEncoder(numBlocks: Int) extends Serializable {
+  private[recommendation] class LocalIndexEncoder(numBlocks: Int) extends Serializable {
 
     require(numBlocks > 0, s"numBlocks must be positive but found $numBlocks.")
 

mllib/src/test/scala/org/apache/spark/ml/recommendation/ALSSuite.scala

@@ -0,0 +1,44 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.ml.recommendation
+
+import java.util.Random
+
+import org.scalatest.FunSuite
+
+import org.apache.spark.ml.recommendation.ALS.LocalIndexEncoder
+import org.apache.spark.mllib.util.MLlibTestSparkContext
+
+class ALSSuite extends FunSuite with MLlibTestSparkContext {
+
+  test("local index encoder") {
+    val random = new Random
+    for (numBlocks <- Seq(1, 2, 5, 10, 20, 50, 100)) {
+      val encoder = new LocalIndexEncoder(numBlocks)
+      val maxLocalIndex = Int.MaxValue / numBlocks
+      val tests = Seq.fill(5)((random.nextInt(numBlocks), random.nextInt(maxLocalIndex))) ++
+        Seq((0, 0), (numBlocks - 1, maxLocalIndex))
+      tests.foreach { case (blockId, localIndex) =>
+        val err = s"Failed with numBlocks=$numBlocks, blockId=$blockId, and localIndex=$localIndex."
+        val encoded = encoder.encode(blockId, localIndex)
+        assert(encoder.blockId(encoded) === blockId, err)
+        assert(encoder.localIndex(encoded) === localIndex, err)
+      }
+    }
+  }
+}