diff -r 4ebc2e2fb97c -r 71c04702a3d5 test/jdk/java/util/StringJoiner/MergeTest.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/jdk/java/util/StringJoiner/MergeTest.java	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,170 @@
+/*
+ * Copyright (c) 2013, 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.
+ */
+
+/**
+ * @test
+ * @bug 8017231 8020977 8054221
+ * @summary test  StringJoiner::merge
+ * @run testng MergeTest
+ */
+
+import java.util.StringJoiner;
+import java.util.stream.Stream;
+import org.testng.annotations.Test;
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.fail;
+
+@Test
+public class MergeTest {
+    private static final String[] PREFIXES = {"", "{", "@#$%"};
+    private static final String[] SUFFIXES = {"", "}", "*&%$"};
+
+    private static class Fixes {
+        public String pre0, suf0;
+        public String pre1, suf1;
+        public Fixes(String prefix0, String suffix0,
+                     String prefix1, String suffix1) {
+            this.pre0 = prefix0;
+            this.suf0 = suffix0;
+            this.pre1 = prefix1;
+            this.suf1 = suffix1;
+        }
+    }
+
+    private static Stream<Fixes> fixesStream() {
+        Stream.Builder<Fixes> builder = Stream.builder();
+        for (final String prefix0 : PREFIXES) {
+            for (final String suffix0 : SUFFIXES) {
+                for (final String prefix1 : PREFIXES) {
+                    for (final String suffix1 : SUFFIXES) {
+                        builder.accept(new Fixes(prefix0, suffix0,
+                                                 prefix1, suffix1));
+                    }
+                }
+            }
+        }
+        return builder.build();
+    }
+
+    @Test(expectedExceptions = {NullPointerException.class})
+    public void testNull() {
+        StringJoiner sj = new StringJoiner(",", "{", "}");
+        sj.merge(null);
+    }
+
+    public void testSimple() {
+        fixesStream().forEach(fixes -> {
+            StringJoiner sj = new StringJoiner(",", fixes.pre0, fixes.suf0);
+            StringJoiner other = new StringJoiner(",", fixes.pre1, fixes.suf1);
+            Stream.of("a", "b", "c").forEachOrdered(sj::add);
+            Stream.of("d", "e", "f").forEachOrdered(other::add);
+
+            sj.merge(other);
+            assertEquals(sj.toString(), fixes.pre0 + "a,b,c,d,e,f" + fixes.suf0);
+        });
+    }
+
+    public void testEmptyOther() {
+        fixesStream().forEach(fixes -> {
+            StringJoiner sj = new StringJoiner(",", fixes.pre0, fixes.suf0);
+            StringJoiner other = new StringJoiner(",", fixes.pre1, fixes.suf1);
+            Stream.of("a", "b", "c").forEachOrdered(sj::add);
+
+            sj.merge(other);
+            assertEquals(sj.toString(), fixes.pre0 + "a,b,c" + fixes.suf0);
+
+            other.setEmptyValue("EMPTY");
+            sj.merge(other);
+            assertEquals(sj.toString(), fixes.pre0 + "a,b,c" + fixes.suf0);
+        });
+    }
+
+    public void testEmptyThis() {
+        fixesStream().forEach(fixes -> {
+            StringJoiner sj = new StringJoiner(",", fixes.pre0, fixes.suf0);
+            StringJoiner other = new StringJoiner(":", fixes.pre1, fixes.suf1);
+            Stream.of("d", "e", "f").forEachOrdered(other::add);
+
+            sj.merge(other);
+            assertEquals(sj.toString(), fixes.pre0 + "d:e:f" + fixes.suf0);
+
+            sj = new StringJoiner(",", fixes.pre0, fixes.suf0).setEmptyValue("EMPTY");
+            assertEquals(sj.toString(), "EMPTY");
+            sj.merge(other);
+            assertEquals(sj.toString(), fixes.pre0 + "d:e:f" + fixes.suf0);
+        });
+    }
+
+    public void testEmptyBoth() {
+        fixesStream().forEach(fixes -> {
+            StringJoiner sj = new StringJoiner(",", fixes.pre0, fixes.suf0);
+            StringJoiner other = new StringJoiner(":", fixes.pre1, fixes.suf1);
+
+            sj.merge(other);
+            assertEquals(sj.toString(), fixes.pre0 + fixes.suf0);
+
+            other.setEmptyValue("NOTHING");
+            sj.merge(other);
+            assertEquals(sj.toString(), fixes.pre0 + fixes.suf0);
+
+            sj = new StringJoiner(",", fixes.pre0, fixes.suf0).setEmptyValue("EMPTY");
+            assertEquals(sj.toString(), "EMPTY");
+            sj.merge(other);
+            assertEquals(sj.toString(), "EMPTY");
+        });
+    }
+
+    public void testCascadeEmpty() {
+        fixesStream().forEach(fixes -> {
+            StringJoiner sj = new StringJoiner(",", fixes.pre0, fixes.suf0);
+            StringJoiner o1 = new StringJoiner(":", fixes.pre1, fixes.suf1).setEmptyValue("Empty1");
+            StringJoiner o2 = new StringJoiner(",", "<", ">").setEmptyValue("Empty2");
+
+            o1.merge(o2);
+            assertEquals(o1.toString(), "Empty1");
+
+            sj.merge(o1);
+            assertEquals(sj.toString(), fixes.pre0 + fixes.suf0);
+        });
+    }
+
+    public void testDelimiter() {
+        fixesStream().forEach(fixes -> {
+            StringJoiner sj = new StringJoiner(",", fixes.pre0, fixes.suf0);
+            StringJoiner other = new StringJoiner(":", fixes.pre1, fixes.suf1);
+            Stream.of("a", "b", "c").forEachOrdered(sj::add);
+            Stream.of("d", "e", "f").forEachOrdered(other::add);
+
+            sj.merge(other);
+            assertEquals(sj.toString(), fixes.pre0 + "a,b,c,d:e:f" + fixes.suf0);
+        });
+    }
+
+    public void testMergeSelf() {
+        fixesStream().forEach(fixes -> {
+            final StringJoiner sj = new StringJoiner(",", fixes.pre0, fixes.suf0).add("a").add("b");
+            assertEquals(sj.merge(sj).toString(), fixes.pre0 + "a,b,a,b" + fixes.suf0);
+            assertEquals(sj.merge(sj).toString(), fixes.pre0 + "a,b,a,b,a,b,a,b" + fixes.suf0);
+        });
+    }
+}