diff -r 000000000000 -r 6474c204b198 js/src/gdb/tests/test-JSString.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/gdb/tests/test-JSString.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,64 @@
+#include "gdb-tests.h"
+#include "jsatom.h"
+#include "jscntxt.h"
+
+// When JSGC_ANALYSIS is #defined, Rooted<JSFlatString*> needs the definition
+// of JSFlatString in order to figure out its ThingRootKind
+#include "vm/String.h"
+
+FRAGMENT(JSString, simple) {
+  JS::Rooted<JSString *> empty(cx, JS_NewStringCopyN(cx, nullptr, 0));
+  JS::Rooted<JSString *> x(cx, JS_NewStringCopyN(cx, "x", 1));
+  JS::Rooted<JSString *> z(cx, JS_NewStringCopyZ(cx, "z"));
+
+  // I expect this will be a non-inlined string.
+  JS::Rooted<JSString *> stars(cx, JS_NewStringCopyZ(cx,
+                                                     "*************************"
+                                                     "*************************"
+                                                     "*************************"
+                                                     "*************************"));
+
+  // This may well be an inlined string.
+  JS::Rooted<JSString *> xz(cx, JS_ConcatStrings(cx, x, z));
+
+  // This will probably be a rope.
+  JS::Rooted<JSString *> doubleStars(cx, JS_ConcatStrings(cx, stars, stars));
+
+  // Ensure we're not confused by typedefs for pointer types.
+  JSString *xRaw = x;
+
+  breakpoint();
+
+  (void) empty;
+  (void) x;
+  (void) z;
+  (void) stars;
+  (void) xz;
+  (void) doubleStars;
+  (void) xRaw;
+}
+
+FRAGMENT(JSString, null) {
+  JS::Rooted<JSString *> null(cx, nullptr);
+  JSString *nullRaw = null;
+
+  breakpoint();
+
+  (void) null;
+  (void) nullRaw;
+}
+
+FRAGMENT(JSString, subclasses) {
+  JS::Rooted<JSFlatString *> flat(cx, JS_FlattenString(cx, JS_NewStringCopyZ(cx, "Hi!")));
+
+  breakpoint();
+
+  (void) flat;
+}
+
+FRAGMENT(JSString, atom) {
+  JSAtom *molybdenum = js::Atomize(cx, "molybdenum", 10);
+  breakpoint();
+
+  (void) molybdenum;
+}