Mocking SignalR Client for better Unit Testing

Last Updated: January 22, 2015 | Created: June 10, 2014

Modal dialog showing task progress.
Modal dialog showing task progress. Uses SignalR.

Why I needed to Mock SignalR

I build geographic modelling applications and they have lots of tasks that take a long time, sometime many minutes, to run. I am currently  developing an open source framework to help speed up the development of such ASP.NET MVC applications. Therefore part of the framework I have includes modules for handling long running processes, with a progress bar, messages and user cancellation. Click on the image on the left to see a a simple example of a model panel with a green progress bar at the top and a list of sent messages as the task works its way through the calculations (well, in this case a test code so the messages aren’t that exciting) .

I have used SignalR for the communication channel between the JavaScript and the MVC5 server. I have found SignalR to be excellent and makes two-way comms really easy.

However my application is fairly complicated because of all the things that can happen, like errors, user wanting to cancel, losing connection, etc. In particular the JavaScript client uses a state machine to handle all the options, and that needs checking. For this reason I wanted to unit test both ends. (Read my blog on Unit Testing for an in-depth look at how I use Unit Testing).

The C# end was fairly straight forward to test, as it was partitioned well. However for the JavaScript end I needed to Mock the SignalR JavaScript library. I could not find anything online so I wrote something myself.

Mocking the SignalR JavaScript Client

I turns out that is wasn’t that hard to mock the SignalR Client, although I should say I don’t use the autogenerated SignalR hub scripts, but use the createHubProxy(‘HubName’) as I find that easier to manage that loading a dynamically created script. I have listed the code mocked SignalR Client code below:

//This is a mock for a small part of SignalR's javascript client.
//This code does not mock autogenerated SignalR hub scripts as the
//ActionRunner code uses the connection.createHubProxy('HubName') method,
//followed by .on or .invoke to setup the receive and send methods respectively

var mockSignalRClient = (function ($) {

    var mock = {};

    //first the items used by unit testing to see what has happened
    mock.callLog = null;
    mock.onFunctionDict = null;
    mock.doneFunc = null;
    mock.failFunc = null;
    mock.errorFunc = null;
    //This logs a string with the caller's function name and the parameters
    //you must provide the function name, but it finds the function arguments itself
    mock.logStep = function (funcName) {
        var log = funcName + '(';
        var callerArgs = arguments.callee.caller.arguments;
        for (var i = 0; i < callerArgs.length; i++) {
            log += (typeof callerArgs[i] === 'function') ? 'function, ' : callerArgs[i] + ', ';
        if (callerArgs.length > 0)
            log = log.substr(0, log.length - 2);
        mock.callLog.push(log + ')');
    mock.reset = function() {
        mock.callLog = [];
        mock.onFunctionDict = {}
        mock.doneFunc = null;
        mock.failFunc = null;
        mock.errorFunc = null;

    //doneFail is the object returned by connection.start()
    var doneFail = {};
    doneFail.done = function (startFunc) {
        mock.doneFunc = startFunc;
        return doneFail;
    }; = function(failFunc) {
        mock.failFunc = failFunc;
        return doneFail;

    //Channel is the object returned by connection.createHubProxy
    var channel = {};
    channel.on = function (namedMessage, functionToCall) {
        mock.onFunctionDict[namedMessage] = functionToCall;
    channel.invoke = function (actionName, actionGuid) {

    //connection is the object returned by $.hubConnection
    var connection = {};
    connection.createHubProxy = function (hubName) {
        return channel;
    connection.error = function (errorFunc) {
        mock.errorFunc = errorFunc;
    connection.start = function () {
        return doneFail;
    connection.stop = function () {
        return doneFail;

    //now we run once the method to add the hubConnection function to jQuery
    $.hubConnection = function() {
        return connection;

    //Return the mock base which has all the error feedback information in it
    return mock;


I think you will find most of this fairly easy to understand. Lines 8 to 34 are all the variables and methods for Unit Testing to use. The rest of the code implements the methods which mock the SignalR methods I use in my code.

How did I use this Mock SignalR?

SignalR works by adding .hubConnection() to jQuery so it was simple to make the mock SignalR client do the same (see line 71 above). My actual code checks that jQuery is present and then that $.hubConnection is defined, which ensures SignalR is loaded. Here is a piece of code from my ActionRunner.comms.js that does the initial setup to see how it uses SignalR and therefore what I needed to Mock.

//This deals with setting up the SignalR connections and events
function setupTaskChannel() {


    actionRunner.numErrorMessages = 0;

    //Setup connection and actionChannel with the functions to call
    var connection = $.hubConnection();

    //connection.logging = true;
    actionChannel = connection.createHubProxy('ActionHub');

    //Now make sure connection errors are handled
    connection.error(function(error) {
        actionRunner.reportSystemError('SignalR error: ' + error);
    //and start the connection and send the start message
        .done(function() {
        .fail(function(error) {
            actionRunner.reportSystemError('SignalR connection error: ' + error);
Jasmine Unit Test checking what SignalR functions were called
Jasmine Unit Test checking what SignalR functions were called

Using this mocking framework

There are two main ways I use it. Firstly you get a log of each method called, which helps ensure the right methods are called.

Secondly most of the calls to SignalR link functions to certain SignalR events. By capturing these functions the unit test can call them to simulate SignalR messages, errors etc. That allows a very good level of checking.

Getting the whole picture

In case you are interested in downloading the code or seeing how it was used then here are a series of links to various bits of code. These are taken form an open source project that I am currently working on, so the code is subject to change. I have listed all the various parts of the testing. UPDATE: These links had broken because the git repository had changed – sorry about that. Now fixed.


As I said in my previous post ‘Unit Testing in C# and JavaScript‘ I find mocking in JavaScript very easy and helpful. The ActionRunner is complex enough to need unit testing and I found mocking the various parts I wanted to replace fairly quick to implement.

I hope this helps you with SignalR and encourages you to mock other frameworks to help you test more easily. Happy coding.