[SPARK-10012] [ML] Missing test case for Params#arrayLengthGt

Currently there is no test case for `Params#arrayLengthGt`.

Author: lewuathe <lewuathe@me.com>

Closes #8223 from Lewuathe/SPARK-10012.

mllib/src/test/scala/org/apache/spark/ml/param/ParamsSuite.scala

@@ -199,6 +199,9 @@ class ParamsSuite extends SparkFunSuite {
 
     val inArray = ParamValidators.inArray[Int](Array(1, 2))
     assert(inArray(1) && inArray(2) && !inArray(0))
+
+    val arrayLengthGt = ParamValidators.arrayLengthGt[Int](2.0)
+    assert(arrayLengthGt(Array(0, 1, 2)) && !arrayLengthGt(Array(0, 1)))
   }
 
   test("Params.copyValues") {