add runtime test

test/runtime.js

@@ -0,0 +1,15 @@
+var runtime = require("../lib/6to5/runtime");
+var assert  = require("assert");
+
+suite("runtime", function () {
+  test("default", function () {
+    var code = runtime();
+    assert.ok(!!code.match(/to5Runtime/));
+  });
+
+  test("custom", function () {
+    var code = runtime("customNamespace");
+    assert.ok(code.match(/customNamespace/));
+    assert.ok(!code.match(/to5Runtime/));
+  });
+});