diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/debug/Debugger-debuggees-08.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/debug/Debugger-debuggees-08.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,25 @@
+// Adding a debuggee more than once is redundant.
+
+var dbg = new Debugger;
+var g = newGlobal();
+var w = dbg.addDebuggee(g);
+assertEq(w instanceof Debugger.Object, true);
+
+function usual() {
+    assertEq(dbg.hasDebuggee(g), true);
+    assertEq(dbg.hasDebuggee(w), true);
+    var arr = dbg.getDebuggees();
+    assertEq(arr.length, 1);
+    assertEq(arr[0], w);
+}
+
+usual();
+assertEq(dbg.addDebuggee(g), w);
+usual();
+assertEq(dbg.addDebuggee(w), w);
+usual();
+
+// Removing the debuggee once is enough.
+assertEq(dbg.removeDebuggee(g), undefined);
+assertEq(dbg.hasDebuggee(g), false);
+assertEq(dbg.getDebuggees().length, 0);