fix(backend): Use Use fakeTimers() in tests to resolve test flakiness

The tests were failing from time to time due to difference in the dates
in the error messages asserted in the assertions test files.
The difference was 1 second.

.changeset/shiny-meals-marry.md

@@ -0,0 +1,5 @@
+---
+'@clerk/backend': patch
+---
+
+Fix 1 second flakiness in assertions tests

packages/backend/src/tokens/jwt/assertions.test.ts

@@ -14,7 +14,7 @@ import {
 } from './assertions';
 
 export default (QUnit: QUnit) => {
-  const { module, test, hooks } = QUnit;
+  const { module, test } = QUnit;
 
   function formatToUTCString(ts: number) {
     const tsDate = new Date(0);
@@ -259,7 +259,16 @@ export default (QUnit: QUnit) => {
     });
   });
 
-  module('assertExpirationClaim(exp, clockSkewInMs)', () => {
+  module('assertExpirationClaim(exp, clockSkewInMs)', hooks => {
+    let fakeClock;
+    hooks.beforeEach(() => {
+      fakeClock = sinon.useFakeTimers();
+    });
+    hooks.afterEach(() => {
+      fakeClock.restore();
+      sinon.restore();
+    });
+
     test('throws err if exp is in the past', assert => {
       const nowInSeconds = Date.now() / 1000;
       const exp = nowInSeconds - 5;
@@ -300,7 +309,16 @@ export default (QUnit: QUnit) => {
     });
   });
 
-  module('assertActivationClaim(nbf, clockSkewInMs)', () => {
+  module('assertActivationClaim(nbf, clockSkewInMs)', hooks => {
+    let fakeClock;
+    hooks.beforeEach(() => {
+      fakeClock = sinon.useFakeTimers();
+    });
+    hooks.afterEach(() => {
+      fakeClock.restore();
+      sinon.restore();
+    });
+
     test('does not throw error if nbf is undefined', assert => {
       assert.equal(undefined, assertActivationClaim(undefined, 0));
     });
@@ -343,7 +361,16 @@ export default (QUnit: QUnit) => {
     });
   });
 
-  module('assertIssuedAtClaim(iat, clockSkewInMs)', () => {
+  module('assertIssuedAtClaim(iat, clockSkewInMs)', hooks => {
+    let fakeClock;
+    hooks.beforeEach(() => {
+      fakeClock = sinon.useFakeTimers();
+    });
+    hooks.afterEach(() => {
+      fakeClock.restore();
+      sinon.restore();
+    });
+
     test('does not throw error if iat is undefined', assert => {
       assert.equal(undefined, assertIssuedAtClaim(undefined, 0));
     });