Add ResetSystemProperties test fixture mixin; use it in SparkSubmitSu…

…ite.

core/src/test/scala/org/apache/spark/deploy/SparkSubmitSuite.scala

@@ -23,11 +23,11 @@ import scala.collection.mutable.ArrayBuffer
 
 import org.apache.spark._
 import org.apache.spark.deploy.SparkSubmit._
-import org.apache.spark.util.Utils
+import org.apache.spark.util.{ResetSystemProperties, Utils}
 import org.scalatest.FunSuite
 import org.scalatest.Matchers
 
-class SparkSubmitSuite extends FunSuite with Matchers {
+class SparkSubmitSuite extends FunSuite with Matchers with ResetSystemProperties {
   def beforeAll() {
     System.setProperty("spark.testing", "true")
   }

core/src/test/scala/org/apache/spark/util/ResetSystemProperties.scala

@@ -0,0 +1,41 @@
+/*
+ * 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.util
+
+import java.util.Properties
+
+import org.scalatest.{Suite, SuiteMixin}
+
+
+/**
+ * Mixin for automatically resetting system properties that are modified in ScalaTest tests.
+ * This resets the properties after each individual test.
+ *
+ * See the "Composing fixtures by stacking traits" section at
+ * http://www.scalatest.org/user_guide/sharing_fixtures for more details about this pattern.
+ */
+private[spark] trait ResetSystemProperties extends SuiteMixin { this: Suite =>
+  abstract override def withFixture(test: NoArgTest) = {
+    val oldProperties = new Properties(System.getProperties)
+    try {
+      super.withFixture(test)
+    } finally {
+      System.setProperties(oldProperties)
+    }
+  }
+}