diff --git a/app/assets/javascripts/timeoutPopup.js b/app/assets/javascripts/timeoutPopup.js
index be64d7d22..f8b5b4cee 100644
--- a/app/assets/javascripts/timeoutPopup.js
+++ b/app/assets/javascripts/timeoutPopup.js
@@ -1,25 +1,23 @@
 (function(global) {
     "use strict";
+
     const sessionTimer = document.getElementById("sessionTimer");
 
-    setTimeout(function() {
-        var timeTillSessionEnd = new Date().getTime() + (5 * 60 * 1000);
-        var x = setInterval(function() {
-            var now = new Date().getTime();
-            var difference = timeTillSessionEnd - now;
-            var minutes = Math.floor((difference % (1000 * 60 * 60)) / (1000 * 60));
-            var seconds = Math.floor((difference % (1000 * 60)) / 1000);
-            document.getElementById("timeLeft").innerHTML = + minutes + "m " + seconds + "s";
-            showTimer();
-            document.getElementById("logOutTimer").addEventListener("click", logoutUser);
-            document.getElementById("extendSessionTimer").addEventListener("click", extendSession);
-            if (difference < 0) {
-                clearInterval(x);
-                closeTimer();
-                logoutUser();
-            }
-        }, 1000);
-    }, 25 * 60 * 1000);
+    function checkTimer(timeTillSessionEnd) {
+        var now = new Date().getTime();
+        var difference = timeTillSessionEnd - now;
+        var minutes = Math.floor((difference % (1000 * 60 * 60)) / (1000 * 60));
+        var seconds = Math.floor((difference % (1000 * 60)) / 1000);
+        document.getElementById("timeLeft").innerHTML = + minutes + "m " + seconds + "s";
+        showTimer();
+        document.getElementById("logOutTimer").addEventListener("click", logoutUser);
+        document.getElementById("extendSessionTimer").addEventListener("click", extendSession);
+        if (difference < 0) {
+            clearInterval(x);
+            closeTimer();
+            logoutUser();
+        }
+    }
 
     function logoutUser() {
         window.location.href = '/sign-out';
@@ -36,9 +34,17 @@
     function closeTimer() {
         sessionTimer.close();
     }
-    })(window);
-
-
-
 
+    global.GOVUK.Modules.TimeoutPopup = function() {
+        setTimeout(function() {
+            var timeTillSessionEnd = new Date().getTime() + (5 * 60 * 1000);
+            var x = setInterval(checkTimer, 1000, timeTillSessionEnd);
+        }, 25 * 60 * 1000);
+    };
 
+    global.GOVUK.Modules.TimeoutPopup.checkTimer = checkTimer;
+    global.GOVUK.Modules.TimeoutPopup.logoutUser = logoutUser;
+    global.GOVUK.Modules.TimeoutPopup.extendSession = extendSession;
+    global.GOVUK.Modules.TimeoutPopup.showTimer = showTimer;
+    global.GOVUK.Modules.TimeoutPopup.closeTimer = closeTimer;
+})(window);
diff --git a/tests/javascripts/timeoutPopup.test.js b/tests/javascripts/timeoutPopup.test.js
index 74373de5a..46d88b7d2 100644
--- a/tests/javascripts/timeoutPopup.test.js
+++ b/tests/javascripts/timeoutPopup.test.js
@@ -1,18 +1,97 @@
-const sessionTimerWrapper = require('../../app/assets/javascripts/timeoutPopup.js');
+beforeAll(() => {
+    jest.useFakeTimers();
+    jest.spyOn(global, 'setTimeout');
+
+    document.body.innerHTML = `
+        <dialog class="usa-modal" id="sessionTimer" aria-labelledby="sessionTimerHeading" aria-describedby="timerWarning">
+            <div class="usa-modal__content">
+                <div class="usa-modal__main">
+                <h2 class="usa-modal__heading" id="sessionTimerHeading">
+                    Your session will end soon.
+                    <span class="usa-sr-only">Please choose to extend your session or sign out. Your session will expire in 5 minutes or less.</span>
+                </h2>
+                <div class="usa-prose">
+                    <p>You have been inactive for too long.
+                    Your session will expire in <span id="timeLeft" role="timer"></span>.
+                    </p>
+                </div>
+                <div class="usa-modal__footer">
+                    <ul class="usa-button-group">
+                    <li class="usa-button-group__item">
+                        <button type="button" class="usa-button" id="extendSessionTimer" data-close-modal>
+                        Extend Session
+                        </button>
+                    </li>
+                    <li class="usa-button-group__item">
+                        <button type="button" class="usa-button usa-button--unstyled padding-105 text-center" id="logOutTimer"
+                        data-close-modal>
+                        Sign out
+                        </button>
+                    </li>
+                    </ul>
+                </div>
+                </div>
+            </div>
+        </dialog>
+    `
+
+        const sessionTimerModule = require('../../app/assets/javascripts/timeoutPopup.js');
+        window.GOVUK.modules.start();
+});
+
+afterAll(() => {
+    jest.useRealTimers();
+    document.body.innerHTML = '';
+});
 
 
-describe('Test popup process', () => {
-    beforeEach(() => {
-        jest.useFakeTimers();
-    });
-
-    afterEach(() => {
-        jest.useRealTimers();
-    });
-
-    it('Test timers work', () => {
+describe('When an authenticated user', () => {
+    test('does whatever', () => {
         jest.runAllTimers();
     });
 
-}); 
+});
 
+
+describe('The session timer ', () => {
+    test('logoutUser method logs the user out', () => {
+        const logoutUserMethod = window.GOVUK.Modules.TimeoutPopup.logoutUser;
+
+        expect(window.location.href).toEqual(expect.not.stringContaining('/sign-out'));
+
+        logoutUserMethod();
+
+        expect(window.location.href).toEqual(expect.stringContaining('/sign-out'));
+    });
+
+    test('extendSession method reloads the page', () => {
+        const windowReload = jest.spyOn(window.location, 'reload');
+        const extendSessionMethod = window.GOVUK.Modules.TimeoutPopup.extendSession;
+
+        extendSessionMethod();
+
+        expect(windowReload).toHaveBeenCalled();
+    });
+
+    test('showTimer method shows the session timer modal', () => {
+        const sessionTimer = document.getElementById("sessionTimer");
+        sessionTimer.showModal = jest.fn();
+
+        const showTimerMock = jest.spyOn(sessionTimer, 'showModal');
+
+        window.GOVUK.Modules.TimeoutPopup.showTimer();
+
+        expect(showTimerMock).toHaveBeenCalled();
+    });
+
+    test('closeTimer method closes the session timer modal', () => {
+        const sessionTimer = document.getElementById("sessionTimer");
+        sessionTimer.close = jest.fn();
+
+        const closeTimerMock = jest.spyOn(sessionTimer, 'close');
+
+        window.GOVUK.Modules.TimeoutPopup.closeTimer();
+
+        expect(closeTimerMock).toHaveBeenCalled();
+    });
+});