diff -r 000000000000 -r 6474c204b198 services/sync/tests/unit/test_service_checkAccount.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/services/sync/tests/unit/test_service_checkAccount.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,41 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+Cu.import("resource://services-sync/service.js");
+Cu.import("resource://services-sync/util.js");
+Cu.import("resource://testing-common/services/sync/utils.js");
+
+function run_test() {
+  do_test_pending();
+  ensureLegacyIdentityManager();
+  let server = httpd_setup({
+    "/user/1.0/johndoe": httpd_handler(200, "OK", "1"),
+    "/user/1.0/janedoe": httpd_handler(200, "OK", "0"),
+    // john@doe.com
+    "/user/1.0/7wohs32cngzuqt466q3ge7indszva4of": httpd_handler(200, "OK", "0"),
+    // jane@doe.com
+    "/user/1.0/vuuf3eqgloxpxmzph27f5a6ve7gzlrms": httpd_handler(200, "OK", "1")
+  });
+  try {
+    Service.serverURL = server.baseURI;
+
+    _("A 404 will be recorded as 'generic-server-error'");
+    do_check_eq(Service.checkAccount("jimdoe"), "generic-server-error");
+
+    _("Account that's available.");
+    do_check_eq(Service.checkAccount("john@doe.com"), "available");
+
+    _("Account that's not available.");
+    do_check_eq(Service.checkAccount("jane@doe.com"), "notAvailable");
+
+    _("Username fallback: Account that's not available.");
+    do_check_eq(Service.checkAccount("johndoe"), "notAvailable");
+
+    _("Username fallback: Account that's available.");
+    do_check_eq(Service.checkAccount("janedoe"), "available");
+
+  } finally {
+    Svc.Prefs.resetBranch("");
+    server.stop(do_test_finished);
+  }
+}