--- /dev/null	2018-11-30 10:10:44.238550338 +0100
+++ new/test/hotspot/jtreg/gc/shenandoah/options/TestExplicitGC.java	2018-11-30 21:09:52.130416069 +0100
@@ -0,0 +1,167 @@
+/*
+ * Copyright (c) 2017, 2018, Red Hat, Inc. All rights reserved.
+ *
+ * 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.
+ *
+ */
+
+/*
+ * @test TestExplicitGC
+ * @summary Test that Shenandoah reacts to explicit GC flags appropriately
+ * @key gc
+ * @requires vm.gc.Shenandoah
+ * @library /test/lib
+ * @modules java.base/jdk.internal.misc
+ *          java.management
+ * @run driver TestExplicitGC
+ */
+
+import jdk.test.lib.process.ProcessTools;
+import jdk.test.lib.process.OutputAnalyzer;
+
+public class TestExplicitGC {
+
+    enum Mode {
+        PRODUCT,
+        DIAGNOSTIC,
+        EXPERIMENTAL,
+    }
+
+    public static void main(String[] args) throws Exception {
+        if (args.length > 0) {
+            System.out.println("Calling System.gc()");
+            System.gc();
+            return;
+        }
+
+        String[] full = new String[] {
+                "Pause Full"
+        };
+
+        String[] concNormal = new String[] {
+                "Pause Init Mark",
+                "Pause Final Mark",
+        };
+
+        String[] concTraversal = new String[] {
+                "Pause Init Traversal",
+                "Pause Final Traversal",
+        };
+
+        {
+            ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
+                    "-XX:+UnlockExperimentalVMOptions",
+                    "-XX:+UseShenandoahGC",
+                    "-Xlog:gc",
+                    TestExplicitGC.class.getName(),
+                    "test");
+            OutputAnalyzer output = new OutputAnalyzer(pb.start());
+            for (String p : full) {
+                output.shouldNotContain(p);
+            }
+            for (String p : concNormal) {
+                output.shouldContain(p);
+            }
+            for (String p : concTraversal) {
+                output.shouldNotContain(p);
+            }
+        }
+
+        {
+            ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
+                    "-XX:+UnlockExperimentalVMOptions",
+                    "-XX:+UseShenandoahGC",
+                    "-Xlog:gc",
+                    "-XX:+DisableExplicitGC",
+                    TestExplicitGC.class.getName(),
+                    "test");
+            OutputAnalyzer output = new OutputAnalyzer(pb.start());
+            for (String p : full) {
+                output.shouldNotContain(p);
+            }
+            for (String p : concNormal) {
+                output.shouldNotContain(p);
+            }
+            for (String p : concTraversal) {
+                output.shouldNotContain(p);
+            }
+        }
+
+        {
+            ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
+                    "-XX:+UnlockExperimentalVMOptions",
+                    "-XX:+UseShenandoahGC",
+                    "-Xlog:gc",
+                    "-XX:+ExplicitGCInvokesConcurrent",
+                    TestExplicitGC.class.getName(),
+                    "test");
+            OutputAnalyzer output = new OutputAnalyzer(pb.start());
+            for (String p : full) {
+                output.shouldNotContain(p);
+            }
+            for (String p : concNormal) {
+                output.shouldContain(p);
+            }
+            for (String p : concTraversal) {
+                output.shouldNotContain(p);
+            }
+        }
+
+        {
+            ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
+                    "-XX:+UnlockExperimentalVMOptions",
+                    "-XX:+UseShenandoahGC",
+                    "-Xlog:gc",
+                    "-XX:+ExplicitGCInvokesConcurrent",
+                    "-XX:ShenandoahGCHeuristics=traversal",
+                    TestExplicitGC.class.getName(),
+                    "test");
+            OutputAnalyzer output = new OutputAnalyzer(pb.start());
+            for (String p : full) {
+                output.shouldNotContain(p);
+            }
+            for (String p : concNormal) {
+                output.shouldNotContain(p);
+            }
+            for (String p : concTraversal) {
+                output.shouldContain(p);
+            }
+        }
+
+        {
+            ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
+                    "-XX:+UnlockExperimentalVMOptions",
+                    "-XX:+UseShenandoahGC",
+                    "-Xlog:gc",
+                    "-XX:-ExplicitGCInvokesConcurrent",
+                    TestExplicitGC.class.getName(),
+                    "test");
+            OutputAnalyzer output = new OutputAnalyzer(pb.start());
+            for (String p : full) {
+                output.shouldContain(p);
+            }
+            for (String p : concNormal) {
+                output.shouldNotContain(p);
+            }
+            for (String p : concTraversal) {
+                output.shouldNotContain(p);
+            }
+        }
+    }
+}