diff -r 000000000000 -r 6474c204b198 js/src/gdb/tests/test-Root.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/gdb/tests/test-Root.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,19 @@
+# Test printing Handles.
+
+assert_subprinter_registered('SpiderMonkey', 'instantiations-of-JS::Rooted')
+assert_subprinter_registered('SpiderMonkey', 'instantiations-of-JS::Handle')
+assert_subprinter_registered('SpiderMonkey', 'instantiations-of-JS::MutableHandle')
+assert_subprinter_registered('SpiderMonkey', 'instantiations-of-js::EncapsulatedPtr')
+assert_subprinter_registered('SpiderMonkey', 'js::EncapsulatedValue')
+
+run_fragment('Root.handle')
+
+assert_pretty('obj', '(JSObject * const)  [object global] delegate')
+assert_pretty('mutableObj', '(JSObject *)  [object global] delegate')
+
+run_fragment('Root.HeapSlot')
+
+# This depends on implementation details of arrays, but since HeapSlot is
+# not a public type, I'm not sure how to avoid doing *something* ugly.
+assert_pretty('array->elements[0]', '$jsval("plinth")')
+