added a test as suggested by JoshRosen

sql/core/src/test/scala/org/apache/spark/sql/execution/AggregateSuite.scala

@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution
+
+import org.apache.spark.SparkEnv
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.test.TestSQLContext
+import org.apache.spark.sql.types.DataTypes._
+
+class AggregateSuite extends SparkPlanTest {
+
+  test("SPARK-8357 Memory leakage on unsafe aggregation path with empty input") {
+
+    val df = Seq.empty[(String, Int, Double)].toDF("a", "b", "c")
+
+    val groupExpr = df.col("b").expr
+    val aggrExpr = Alias(Count(Cast(groupExpr, LongType)), "Count")()
+
+    SparkEnv.get.conf.set("spark.unsafe.exceptionOnMemoryLeak", "true")
+    for (codegen <- Seq(false, true); partial <- Seq(false, true); unsafe <- Seq(false, true)) {
+      TestSQLContext.conf.setConfString("spark.sql.codegen", String.valueOf(codegen))
+      checkAnswer(
+        df,
+        GeneratedAggregate(partial, groupExpr :: Nil, aggrExpr :: Nil, unsafe, _: SparkPlan),
+        Seq.empty[(String, Int, Double)])
+    }
+  }
+}