[SPARK-14164][MLLIB] Improve input layer validation of MultilayerPerceptronClassifier

## What changes were proposed in this pull request?

This issue improves an input layer validation and adds related testcases to MultilayerPerceptronClassifier.

```scala
-    // TODO: how to check ALSO that all elements are greater than 0?
-    ParamValidators.arrayLengthGt(1)
+    (t: Array[Int]) => t.forall(ParamValidators.gt(0)) && t.length > 1
```

## How was this patch tested?

Pass the Jenkins tests including the new testcases.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11964 from dongjoon-hyun/SPARK-14164.

1 files changed, 17 insertions, 0 deletions

diff --git a/mllib/src/test/scala/org/apache/spark/ml/classification/MultilayerPerceptronClassifierSuite.scala b/mllib/src/test/scala/org/apache/spark/ml/classification/MultilayerPerceptronClassifierSuite.scala
index 5df8e6a847..53c7a559e3 100644
--- a/mllib/src/test/scala/org/apache/spark/ml/classification/MultilayerPerceptronClassifierSuite.scala
+++ b/mllib/src/test/scala/org/apache/spark/ml/classification/MultilayerPerceptronClassifierSuite.scala
@@ -43,6 +43,23 @@ class MultilayerPerceptronClassifierSuite
     ).toDF("features", "label")
   }
 
+  test("Input Validation") {
+    val mlpc = new MultilayerPerceptronClassifier()
+    intercept[IllegalArgumentException] {
+      mlpc.setLayers(Array[Int]())
+    }
+    intercept[IllegalArgumentException] {
+      mlpc.setLayers(Array[Int](1))
+    }
+    intercept[IllegalArgumentException] {
+      mlpc.setLayers(Array[Int](0, 1))
+    }
+    intercept[IllegalArgumentException] {
+      mlpc.setLayers(Array[Int](1, 0))
+    }
+    mlpc.setLayers(Array[Int](1, 1))
+  }
+
   test("XOR function learning as binary classification problem with two outputs.") {
     val layers = Array[Int](2, 5, 2)
     val trainer = new MultilayerPerceptronClassifier()