[SPARK-15206][SQL] add testcases for distinct aggregate in having clause

## What changes were proposed in this pull request?
Add new test cases for including distinct aggregate in having clause in 2.0 branch.
This is a followup PR for [#12974](https://github.com/apache/spark/pull/12974), which is for 1.6 branch.

Author: xin Wu <xinwu@us.ibm.com>

Closes #12984 from xwu0226/SPARK-15206.

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

@@ -958,6 +958,37 @@ abstract class AggregationQuerySuite extends QueryTest with SQLTestUtils with Te
         Row(11) :: Nil)
     }
   }
+
+  test("SPARK-15206: single distinct aggregate function in having clause") {
+    checkAnswer(
+      sql(
+        """
+          |select key, count(distinct value1)
+          |from agg2 group by key
+          |having count(distinct value1) > 0
+        """.stripMargin),
+      Seq(
+        Row(null, 3),
+        Row(1, 2),
+        Row(2, 2)
+      )
+    )
+  }
+
+  test("SPARK-15206: multiple distinct aggregate function in having clause") {
+    checkAnswer(
+      sql(
+        """
+          |select key, count(distinct value1), count(distinct value2)
+          |from agg2 group by key
+          |having count(distinct value1) > 0 and count(distinct value2) = 3
+        """.stripMargin),
+      Seq(
+        Row(null, 3, 3),
+        Row(1, 2, 3)
+      )
+    )
+  }
 }