add a test

Author: yaooqinn

sql/core/src/test/scala/org/apache/spark/sql/CharVarcharTestSuite.scala

@@ -481,6 +481,8 @@ trait CharVarcharTestSuite extends QueryTest with SQLTestUtils {
       sql("INSERT INTO t VALUES ('c', 1)")
       checkAnswer(sql("SELECT substr(v, 1, 2), sum(i) FROM t GROUP BY v ORDER BY substr(v, 1, 2)"),
         Row("c", 1))
+      checkAnswer(sql("SELECT sum(i) FROM t GROUP BY v ORDER BY substr(v, 1, 2)"),
+        Row(1))
     }
   }
 }