diff -r 000000000000 -r 6474c204b198 js/src/jsapi-tests/testStringBuffer.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jsapi-tests/testStringBuffer.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,29 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "jsatom.h"
+
+#include "jsapi-tests/tests.h"
+#include "vm/StringBuffer.h"
+
+BEGIN_TEST(testStringBuffer_finishString)
+{
+    JSString *str = JS_NewStringCopyZ(cx, "foopy");
+    CHECK(str);
+
+    JS::Rooted<JSAtom*> atom(cx, js::AtomizeString(cx, str));
+    CHECK(atom);
+
+    js::StringBuffer buffer(cx);
+    CHECK(buffer.append("foopy"));
+
+    JS::Rooted<JSAtom*> finishedAtom(cx, buffer.finishAtom());
+    CHECK(finishedAtom);
+    CHECK_EQUAL(atom, finishedAtom);
+    return true;
+}
+END_TEST(testStringBuffer_finishString)