diff --git a/crossfilter/crossfilter-tests.ts b/crossfilter/crossfilter-tests.ts
index 745ed3aa4..8d98bef06 100644
--- a/crossfilter/crossfilter-tests.ts
+++ b/crossfilter/crossfilter-tests.ts
@@ -24,6 +24,11 @@ var payments = crossfilter<Payment>([
   {date: "2011-11-14T17:29:52Z", quantity: 1, total: 200, tip: 100, type: "visa"}
 ]);
 
+var total_payments : number = payments.groupAll<number>().reduce(
+    function(p,v) { return p+=v; },
+    function(p,v) { return p-=v; },
+    function() { return 0; } ).value();
+
 var paymentsByTotal = payments.dimension((d) => d.total);
 
 // Filters