diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/collections/Set-delete-size.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/collections/Set-delete-size.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,15 @@
+// set.delete(v) decrements set.size iff the set contained v.
+
+var s = Set();
+for (var i = 0; i < 10; i++)
+    s.add(i);
+
+for (var i = 10; i > 0; i--) {
+    assertEq(s.size, i);
+    assertEq(s.delete(i), false);
+    assertEq(s.size, i);
+    assertEq(s.delete(i - 1), true);
+    assertEq(s.size, i - 1);
+    assertEq(s.delete(i - 1), false);
+    assertEq(s.size, i - 1);
+}