Add a regression test.

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveQuerySuite.scala

@@ -18,6 +18,7 @@
 package org.apache.spark.sql.hive.execution
 
 import org.apache.spark.sql.hive.test.TestHive._
+import org.apache.spark.sql.hive.test.TestHive
 
 /**
  * A set of test cases expressed in Hive QL that are not covered by the tests included in the hive distribution.
@@ -160,4 +161,14 @@ class HiveQuerySuite extends HiveComparisonTest {
     hql("SELECT * FROM src").toString
   }
 
+  test("SPARK-1704: Explain commands as a SchemaRDD") {
+    hql("CREATE TABLE IF NOT EXISTS src (key INT, value STRING)")
+    val rdd = hql("explain select key, count(value) from src group by key")
+    assert(rdd.collect().size == 1)
+    assert(rdd.toString.contains("ExplainCommand"))
+    assert(rdd.filter(row => row.toString.contains("ExplainCommand")).collect().size == 0,
+      "actual contents of the result should be the plans of the query to be explained")
+    TestHive.reset()
+  }
+
 }