Add definition and test for when.iterate

when/when-tests.ts

@@ -101,6 +101,21 @@ when.settle<number>([when(1), when(2), when.reject(new Error("Foo"))]).then(desc
 	return descriptors.filter(d => d.state === 'rejected').reduce((r, d) => r + d.value, 0);
 });
 
+/* when.iterate(f, predicate, handler, seed) */
+
+when.iterate(function (x) {
+	return x + 1;
+}, function (x) {
+	// Stop when x >= 100000000000
+	return x >= 100000000000;
+}, function (x) {
+	console.log(x);
+}, 0).done(function (x) {
+	console.log(x === 100000000000);
+}, function (err) {
+	console.log(err);
+});
+
 /* when.promise(resolver) */
 
 promise = when.promise<number>(resolve => resolve(5));