[SPARK-13344][TEST] Fix harmless accumulator not found exceptions

See [JIRA](https://issues.apache.org/jira/browse/SPARK-13344) for more detail. This was caused by #10835.

Author: Andrew Or <andrew@databricks.com>

Closes #11222 from andrewor14/fix-test-accum-exceptions.

core/src/test/scala/org/apache/spark/AccumulatorSuite.scala

@@ -34,6 +34,14 @@ import org.apache.spark.serializer.JavaSerializer
 class AccumulatorSuite extends SparkFunSuite with Matchers with LocalSparkContext {
   import AccumulatorParam._
 
+  override def afterEach(): Unit = {
+    try {
+      Accumulators.clear()
+    } finally {
+      super.afterEach()
+    }
+  }
+
   implicit def setAccum[A]: AccumulableParam[mutable.Set[A], A] =
     new AccumulableParam[mutable.Set[A], A] {
       def addInPlace(t1: mutable.Set[A], t2: mutable.Set[A]) : mutable.Set[A] = {

core/src/test/scala/org/apache/spark/InternalAccumulatorSuite.scala

@@ -28,6 +28,14 @@ class InternalAccumulatorSuite extends SparkFunSuite with LocalSparkContext {
   import InternalAccumulator._
   import AccumulatorParam._
 
+  override def afterEach(): Unit = {
+    try {
+      Accumulators.clear()
+    } finally {
+      super.afterEach()
+    }
+  }
+
   test("get param") {
     assert(getParam(EXECUTOR_DESERIALIZE_TIME) === LongAccumulatorParam)
     assert(getParam(EXECUTOR_RUN_TIME) === LongAccumulatorParam)

core/src/test/scala/org/apache/spark/SparkFunSuite.scala

@@ -18,14 +18,26 @@
 package org.apache.spark
 
 // scalastyle:off
-import org.scalatest.{FunSuite, Outcome}
+import org.scalatest.{BeforeAndAfterAll, FunSuite, Outcome}
 
 /**
  * Base abstract class for all unit tests in Spark for handling common functionality.
  */
-private[spark] abstract class SparkFunSuite extends FunSuite with Logging {
+private[spark] abstract class SparkFunSuite
+  extends FunSuite
+  with BeforeAndAfterAll
+  with Logging {
 // scalastyle:on
 
+  protected override def afterAll(): Unit = {
+    try {
+      // Avoid leaking map entries in tests that use accumulators without SparkContext
+      Accumulators.clear()
+    } finally {
+      super.afterAll()
+    }
+  }
+
   /**
    * Log the suite name and the test name before and after each test.
    *
@@ -42,8 +54,6 @@ private[spark] abstract class SparkFunSuite extends FunSuite with Logging {
       test()
     } finally {
       logInfo(s"\n\n===== FINISHED $shortSuiteName: '$testName' =====\n")
-      // Avoid leaking map entries in tests that use accumulators without SparkContext
-      Accumulators.clear()
     }
   }