diff -r 4ebc2e2fb97c -r 71c04702a3d5 test/hotspot/jtreg/gc/concurrent_phase_control/CheckSupported.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/gc/concurrent_phase_control/CheckSupported.java	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 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 gc.concurrent_phase_control;
+
+/*
+ * Utility class that provides verification of expected behavior of
+ * the Concurrent GC Phase Control WB API when the current GC supports
+ * phase control.  The invoking test must provide WhiteBox access.
+ */
+
+import sun.hotspot.WhiteBox;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+public class CheckSupported {
+
+    private static final WhiteBox WB = WhiteBox.getWhiteBox();
+
+    private static Set<String> toSet(List<String> list, String which)
+        throws Exception
+    {
+        Set<String> result = new HashSet<String>(list);
+        if (result.size() < list.size()) {
+            throw new RuntimeException(which + " phases contains duplicates");
+        }
+        return result;
+    }
+
+    private static void checkPhases(String[] expectedPhases) throws Exception {
+        String[] actualPhases = WB.getConcurrentGCPhases();
+
+        List<String> expectedList = Arrays.asList(expectedPhases);
+        List<String> actualList = Arrays.asList(actualPhases);
+
+        Set<String> expected = toSet(expectedList, "Expected");
+        Set<String> actual = toSet(actualList, "Actual");
+
+        expected.removeAll(actualList);
+        actual.removeAll(expectedList);
+
+        boolean match = true;
+        if (!expected.isEmpty()) {
+            match = false;
+            System.out.println("Unexpected phases:");
+            for (String s: expected) {
+                System.out.println("  " + s);
+            }
+        }
+        if (!actual.isEmpty()) {
+            match = false;
+            System.out.println("Expected but missing phases:");
+            for (String s: actual) {
+                System.out.println("  " + s);
+            }
+        }
+        if (!match) {
+            throw new RuntimeException("Mismatch between expected and actual phases");
+        }
+    }
+
+    public static void check(String gcName, String[] phases) throws Exception {
+        // Verify supported.
+        if (!WB.supportsConcurrentGCPhaseControl()) {
+            throw new RuntimeException(
+                gcName + " unexpectedly missing phase control support");
+        }
+
+        checkPhases(phases);
+
+        // Verify IllegalArgumentException thrown by request attempt
+        // with unknown phase.
+        boolean illegalArgumentThrown = false;
+        try {
+            WB.requestConcurrentGCPhase("UNKNOWN PHASE");
+        } catch (IllegalArgumentException e) {
+            // Expected.
+            illegalArgumentThrown = true;
+        } catch (Exception e) {
+            throw new RuntimeException(
+                gcName + ": Unexpected exception when requesting unknown phase: " + e.toString());
+        }
+        if (!illegalArgumentThrown) {
+            throw new RuntimeException(
+                gcName + ": No exception when requesting unknown phase");
+        }
+    }
+}
+