diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/collections/Map-delete.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/collections/Map-delete.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,18 @@
+// Map.prototype.delete works whether the key is present or not.
+
+var m = new Map;
+var key = {};
+
+// when the map is new
+assertEq(m.delete(key), false);
+assertEq(m.has(key), false);
+
+// when the key is present
+assertEq(m.set(key, 'x'), undefined);
+assertEq(m.delete(key), true);
+assertEq(m.has(key), false);
+assertEq(m.get(key), undefined);
+
+// when the key has already been deleted
+assertEq(m.delete(key), false);
+assertEq(m.has(key), false);