--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/jdk.internal.vm.compiler/share/classes/org.graalvm.util.test/src/org/graalvm/util/test/CollectionSizeTest.java	Fri Feb 02 17:28:17 2018 -0800
@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2017, 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.graalvm.util.test;
+
+import static org.junit.Assert.assertEquals;
+
+import org.graalvm.collections.EconomicMap;
+import org.graalvm.collections.Equivalence;
+import org.graalvm.compiler.test.GraalTest;
+import org.graalvm.util.ObjectSizeEstimate;
+import org.junit.Assume;
+import org.junit.Test;
+
+public class CollectionSizeTest {
+
+    /**
+     * Tests the memory size of an empty map and a map with only one or two entries.
+     */
+    @Test
+    public void testSize() {
+        Assume.assumeTrue("Not working in JDK9 due to module visibility.", GraalTest.Java8OrEarlier);
+        EconomicMap<Object, Object> map = EconomicMap.create(Equivalence.IDENTITY);
+        assertEquals(49, ObjectSizeEstimate.forObject(map).getTotalBytes());
+
+        Integer value = 1;
+        map.put(value, value);
+        assertEquals(153, ObjectSizeEstimate.forObject(map).getTotalBytes());
+
+        Integer secondValue = 2;
+        map.put(secondValue, secondValue);
+        assertEquals(153 + 20, ObjectSizeEstimate.forObject(map).getTotalBytes());
+    }
+
+    /**
+     * Tests whether the map actually compresses the entries array when a large number of entries
+     * are deleted.
+     */
+    @Test
+    public void testCompress() {
+        Assume.assumeTrue("Not working in JDK9 due to module visibility.", GraalTest.Java8OrEarlier);
+        EconomicMap<Object, Object> map = EconomicMap.create();
+
+        // Measuring size of map with one entry.
+        Object firstValue = 0;
+        map.put(firstValue, firstValue);
+        ObjectSizeEstimate afterFirstValue = ObjectSizeEstimate.forObject(map);
+
+        // Add 999 more entries.
+        for (int i = 1; i < 1000; ++i) {
+            Object value = i;
+            map.put(value, value);
+        }
+        ObjectSizeEstimate beforeRemove = ObjectSizeEstimate.forObject(map);
+
+        // Remove 999 first entries.
+        for (int i = 0; i < 999; ++i) {
+            map.removeKey(i);
+        }
+        ObjectSizeEstimate afterRemove = ObjectSizeEstimate.forObject(map);
+
+        // Check that size is same size as with one entry.
+        assertEquals(afterFirstValue, afterRemove);
+
+        // Add 999 new entries.
+        for (int i = 0; i < 999; ++i) {
+            Object value = i;
+            map.put(value, value);
+        }
+        ObjectSizeEstimate afterAdd = ObjectSizeEstimate.forObject(map);
+
+        // Check that entries array is same size again.
+        assertEquals(beforeRemove.getPointerCount(), afterAdd.getPointerCount());
+    }
+
+}