--- a/services/sync/modules-testing/fxa_utils.js
+++ b/services/sync/modules-testing/fxa_utils.js
@@ -1,35 +1,23 @@
 "use strict";
 
 this.EXPORTED_SYMBOLS = [
-  "Assert_rejects",
   "initializeIdentityWithTokenServerResponse",
 ];
 
 const {utils: Cu} = Components;
 
 Cu.import("resource://gre/modules/Log.jsm");
 Cu.import("resource://services-sync/main.js");
 Cu.import("resource://services-sync/browserid_identity.js");
 Cu.import("resource://services-common/tokenserverclient.js");
 Cu.import("resource://testing-common/services/common/logging.js");
 Cu.import("resource://testing-common/services/sync/utils.js");
 
-// This shouldn't be here - it should be part of the xpcshell harness.
-// Maybe as Assert.rejects - so we name it like that.
-function Assert_rejects(promise, message) {
-  let deferred = Promise.defer();
-  promise.then(
-    () => deferred.reject(message || "Expected the promise to be rejected"),
-    deferred.resolve
-  );
-  return deferred.promise;
-}
-
 // Create a new browserid_identity object and initialize it with a
 // mocked TokenServerClient which always receives the specified response.
 this.initializeIdentityWithTokenServerResponse = function(response) {
   // First create a mock "request" object that well' hack into the token server.
   // A log for it
   let requestLog = Log.repository.getLogger("testing.mock-rest");
   if (!requestLog.appenders.length) { // might as well see what it says :)
     requestLog.addAppender(new Log.DumpAppender());

--- a/services/sync/tests/unit/test_browserid_identity.js
+++ b/services/sync/tests/unit/test_browserid_identity.js
@@ -264,22 +264,22 @@ add_task(function test_ensureLoggedIn() 
   // arrange for no logged in user.
   let fxa = browseridManager._fxaService
   let signedInUser = fxa.internal.currentAccountState.signedInUser;
   fxa.internal.currentAccountState.signedInUser = null;
   browseridManager.initializeWithCurrentIdentity();
   Assert.ok(!browseridManager._shouldHaveSyncKeyBundle,
             "_shouldHaveSyncKeyBundle should be false so we know we are testing what we think we are.");
   Status.login = LOGIN_FAILED_NO_USERNAME;
-  yield Assert_rejects(browseridManager.ensureLoggedIn(), "expecting rejection due to no user");
+  yield Assert.rejects(browseridManager.ensureLoggedIn(), "expecting rejection due to no user");
   Assert.ok(browseridManager._shouldHaveSyncKeyBundle,
             "_shouldHaveSyncKeyBundle should always be true after ensureLogin completes.");
   fxa.internal.currentAccountState.signedInUser = signedInUser;
   Status.login = LOGIN_FAILED_LOGIN_REJECTED;
-  yield Assert_rejects(browseridManager.ensureLoggedIn(),
+  yield Assert.rejects(browseridManager.ensureLoggedIn(),
                        "LOGIN_FAILED_LOGIN_REJECTED should have caused immediate rejection");
   Assert.equal(Status.login, LOGIN_FAILED_LOGIN_REJECTED,
                "status should remain LOGIN_FAILED_LOGIN_REJECTED");
   Status.login = LOGIN_FAILED_NETWORK_ERROR;
   yield browseridManager.ensureLoggedIn();
   Assert.equal(Status.login, LOGIN_SUCCEEDED, "final ensureLoggedIn worked");
 });
 
@@ -355,33 +355,33 @@ add_task(function test_getTokenErrors() 
   initializeIdentityWithTokenServerResponse({
     status: 401,
     headers: {"content-type": "application/json"},
     body: JSON.stringify({}),
   });
   let browseridManager = Service.identity;
 
   yield browseridManager.initializeWithCurrentIdentity();
-  yield Assert_rejects(browseridManager.whenReadyToAuthenticate.promise,
+  yield Assert.rejects(browseridManager.whenReadyToAuthenticate.promise,
                        "should reject due to 401");
   Assert.equal(Status.login, LOGIN_FAILED_LOGIN_REJECTED, "login was rejected");
 
   // XXX - other interesting responses to return?
 
   // And for good measure, some totally "unexpected" errors - we generally
   // assume these problems are going to magically go away at some point.
   _("Arrange for an empty body with a 200 response - should reflect a network error.");
   initializeIdentityWithTokenServerResponse({
     status: 200,
     headers: [],
     body: "",
   });
   browseridManager = Service.identity;
   yield browseridManager.initializeWithCurrentIdentity();
-  yield Assert_rejects(browseridManager.whenReadyToAuthenticate.promise,
+  yield Assert.rejects(browseridManager.whenReadyToAuthenticate.promise,
                        "should reject due to non-JSON response");
   Assert.equal(Status.login, LOGIN_FAILED_NETWORK_ERROR, "login state is LOGIN_FAILED_NETWORK_ERROR");
 });
 
 add_task(function test_getTokenErrorWithRetry() {
   _("tokenserver sends an observer notification on various backoff headers.");
 
   // Set Sync's backoffInterval to zero - after we simulated the backoff header
@@ -392,17 +392,17 @@ add_task(function test_getTokenErrorWith
     status: 503,
     headers: {"content-type": "application/json",
               "retry-after": "100"},
     body: JSON.stringify({}),
   });
   let browseridManager = Service.identity;
 
   yield browseridManager.initializeWithCurrentIdentity();
-  yield Assert_rejects(browseridManager.whenReadyToAuthenticate.promise,
+  yield Assert.rejects(browseridManager.whenReadyToAuthenticate.promise,
                        "should reject due to 503");
 
   // The observer should have fired - check it got the value in the response.
   Assert.equal(Status.login, LOGIN_FAILED_NETWORK_ERROR, "login was rejected");
   // Sync will have the value in ms with some slop - so check it is at least that.
   Assert.ok(Status.backoffInterval >= 100000);
 
   _("Arrange for a 200 with an X-Backoff header.");
@@ -411,17 +411,17 @@ add_task(function test_getTokenErrorWith
     status: 503,
     headers: {"content-type": "application/json",
               "x-backoff": "200"},
     body: JSON.stringify({}),
   });
   browseridManager = Service.identity;
 
   yield browseridManager.initializeWithCurrentIdentity();
-  yield Assert_rejects(browseridManager.whenReadyToAuthenticate.promise,
+  yield Assert.rejects(browseridManager.whenReadyToAuthenticate.promise,
                        "should reject due to no token in response");
 
   // The observer should have fired - check it got the value in the response.
   Assert.ok(Status.backoffInterval >= 200000);
 });
 
 add_task(function test_getKeysErrorWithBackoff() {
   _("Auth server (via hawk) sends an observer notification on backoff headers.");
@@ -443,17 +443,17 @@ add_task(function test_getKeysErrorWithB
       status: 503,
       headers: {"content-type": "application/json",
                 "x-backoff": "100"},
       body: "{}",
     }
   });
 
   let browseridManager = Service.identity;
-  yield Assert_rejects(browseridManager.whenReadyToAuthenticate.promise,
+  yield Assert.rejects(browseridManager.whenReadyToAuthenticate.promise,
                        "should reject due to 503");
 
   // The observer should have fired - check it got the value in the response.
   Assert.equal(Status.login, LOGIN_FAILED_NETWORK_ERROR, "login was rejected");
   // Sync will have the value in ms with some slop - so check it is at least that.
   Assert.ok(Status.backoffInterval >= 100000);
 });
 
@@ -477,17 +477,17 @@ add_task(function test_getKeysErrorWithR
       status: 503,
       headers: {"content-type": "application/json",
                 "retry-after": "100"},
       body: "{}",
     }
   });
 
   let browseridManager = Service.identity;
-  yield Assert_rejects(browseridManager.whenReadyToAuthenticate.promise,
+  yield Assert.rejects(browseridManager.whenReadyToAuthenticate.promise,
                        "should reject due to 503");
 
   // The observer should have fired - check it got the value in the response.
   Assert.equal(Status.login, LOGIN_FAILED_NETWORK_ERROR, "login was rejected");
   // Sync will have the value in ms with some slop - so check it is at least that.
   Assert.ok(Status.backoffInterval >= 100000);
 });
 
@@ -661,17 +661,17 @@ function* initializeIdentityWithHAWKResp
   let fxa = new FxAccounts(internal);
   fxa.internal.currentAccountState.signedInUser = {
       accountData: config.fxaccount.user,
   };
 
   browseridManager._fxaService = fxa;
   browseridManager._signedInUser = null;
   yield browseridManager.initializeWithCurrentIdentity();
-  yield Assert_rejects(browseridManager.whenReadyToAuthenticate.promise,
+  yield Assert.rejects(browseridManager.whenReadyToAuthenticate.promise,
                        "expecting rejection due to hawk error");
 }
 
 
 function getTimestamp(hawkAuthHeader) {
   return parseInt(/ts="(\d+)"/.exec(hawkAuthHeader)[1], 10) * SECOND_MS;
 }
 

--- a/services/sync/tests/unit/test_fxa_service_cluster.js
+++ b/services/sync/tests/unit/test_fxa_service_cluster.js
@@ -12,32 +12,32 @@ add_task(function test_findCluster() {
   _("_findCluster() throws on 500 errors.");
   initializeIdentityWithTokenServerResponse({
     status: 500,
     headers: [],
     body: "",
   });
 
   yield Service.identity.initializeWithCurrentIdentity();
-  yield Assert_rejects(Service.identity.whenReadyToAuthenticate.promise,
+  yield Assert.rejects(Service.identity.whenReadyToAuthenticate.promise,
                        "should reject due to 500");
 
   Assert.throws(function() {
     Service._clusterManager._findCluster();
   });
 
   _("_findCluster() returns null on authentication errors.");
   initializeIdentityWithTokenServerResponse({
     status: 401,
     headers: {"content-type": "application/json"},
     body: "{}",
   });
 
   yield Service.identity.initializeWithCurrentIdentity();
-  yield Assert_rejects(Service.identity.whenReadyToAuthenticate.promise,
+  yield Assert.rejects(Service.identity.whenReadyToAuthenticate.promise,
                        "should reject due to 401");
 
   cluster = Service._clusterManager._findCluster();
   Assert.strictEqual(cluster, null);
 
   _("_findCluster() works with correct tokenserver response.");
   let endpoint = "http://example.com/something";
   initializeIdentityWithTokenServerResponse({