diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/debug/Environment-setVariable-05.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/debug/Environment-setVariable-05.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,14 @@
+// setVariable can change the types of variables and arguments in functions.
+
+var g = newGlobal();
+g.eval("function f(a) { var b = a + 1; debugger; return a + b; }");
+for (var i = 0; i < 20; i++)
+    assertEq(g.f(i), 2 * i + 1);
+
+var dbg = new Debugger(g);
+dbg.onDebuggerStatement = function (frame) {
+    frame.environment.setVariable("a", "xyz");
+    frame.environment.setVariable("b", "zy");
+};
+for (var i = 0; i < 10; i++)
+    assertEq(g.f(i), "xyzzy");