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diff --git a/core/src/test/scala/org/apache/spark/util/collection/MedianHeapSuite.scala b/core/src/test/scala/org/apache/spark/util/collection/MedianHeapSuite.scala
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+/*
+ * 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.collection
+
+import java.util.NoSuchElementException
+
+import org.apache.spark.SparkFunSuite
+
+class MedianHeapSuite extends SparkFunSuite {
+
+  test("If no numbers in MedianHeap, NoSuchElementException is thrown.") {
+    val medianHeap = new MedianHeap()
+    intercept[NoSuchElementException] {
+      medianHeap.median
+    }
+  }
+
+  test("Median should be correct when size of MedianHeap is even") {
+    val array = Array(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
+    val medianHeap = new MedianHeap()
+    array.foreach(medianHeap.insert(_))
+    assert(medianHeap.size() === 10)
+    assert(medianHeap.median === 4.5)
+  }
+
+  test("Median should be correct when size of MedianHeap is odd") {
+    val array = Array(0, 1, 2, 3, 4, 5, 6, 7, 8)
+    val medianHeap = new MedianHeap()
+    array.foreach(medianHeap.insert(_))
+    assert(medianHeap.size() === 9)
+    assert(medianHeap.median === 4)
+  }
+
+  test("Median should be correct though there are duplicated numbers inside.") {
+    val array = Array(0, 0, 1, 1, 2, 3, 4)
+    val medianHeap = new MedianHeap()
+    array.foreach(medianHeap.insert(_))
+    assert(medianHeap.size === 7)
+    assert(medianHeap.median === 1)
+  }
+
+  test("Median should be correct when input data is skewed.") {
+    val medianHeap = new MedianHeap()
+    (0 until 10).foreach(_ => medianHeap.insert(5))
+    assert(medianHeap.median === 5)
+    (0 until 100).foreach(_ => medianHeap.insert(10))
+    assert(medianHeap.median === 10)
+    (0 until 1000).foreach(_ => medianHeap.insert(0))
+    assert(medianHeap.median === 0)
+  }
+}