unit tests

Azure Mobile App on Azure Friday

Last month I had a pleasure to talk about Azure App with Scott Hanselman on his show Azure Friday.

In this talk I presented Azure App architecture, our CI/CD infrastructure and how we took advantage of various benefits we get thanks to building app with Xamarin. Check it out!

If you want to learn more details about how we built the Azure App, check out my blog post Under the hood of the Azure Mobile App.

My talk was pretty technical. Deep into the meat. However, the same week, Michael Flanakin gave high-level overview of Azure App and our future plans:

Have you tried Azure App yet?

It is available on iOS and Android.

We would love to hear your feedback through our User Voice!

Unit Testing Accessibility

In Web Accessibility Hacker Way I mentioned that “only 20% of accessibility requirements can be verified by tools”. Nevertheless, it is worth to cover this 20%. Especially, when it is not very hard. You know that having automated test that guard against regressions always pays off in a long run.

As of today the best automatic verification tool for accessibility is aXe.


There is aXe Chrome plugin and aXe Firefox plugin that enables you to run accessibility audit manually:

aXe - results

Running automated tool manually is useful, but it is better to run it automatically as unit test, and incorporate it into your Continuous Integration to run it automatically after every commit.

Running accessibility audit with aXe

You can install aXe with npm:

npm i axe-core

The aXe has a function a11yCheck that performs accessibility audit on specified HTML Element. You may run it against widgets or partial views on your web app. That function takes 2 parameters:

  1. HTMLElement to be audited
  2. callback function that is invoked with results parameter
axe.a11yCheck($("#myElement")[0], function (results) {
    results.violations.length && console.error(results.violations);

It is useful to print errors to console, as the results.violations is an array of nested objects with different properties. Many of them are helpful to diagnose the issue.

aXe - console errors

*a11y is abbreviation for accessibility (similar like i18n for internationalization), 11 is number of letters between ‘a’ and ‘y’

Running aXe with Jasmine 2.x

In order to run aXe with Jasmine, you need to take into account that a11yCheck is asynchronous. Thus, you need to pass and invoke done function:

describe("a11y check", function() {
  it("has no accessbility violations (check console for errors)", function(done) {
    axe.a11yCheck($("#myElement")[0], function (results) {
        if (results.violations.length>0) {

Running aXe with QUnit 2.x

It is similar in QUnit. You also need to invoke done function, but first you need to get it by calling assert.async():

QUnit.test("a11y check", function(assert) {
    var done = assert.async();

    axe.a11yCheck($("#myElement")[0], function (results) {
        assert.strictEqual(results.violations.length, 0, "There should be no A11y violations (check console for errors)");
        if (results.violations.length>0) {


I created a sample with button and input tag:

<div id="fixture">
  <button>My button</button> 
  <input type="text" />

This sample is not accessible because input tag does not have a label, and a11yCheck should report violations. The sample code, with Jasmine and QUnit tests, is available on github: axe-unittests.


While automated accessibility unit tests are great, you probably still want to use aXe plugin for Chrome to investigate reported violations. It’s more convenient, and it has neat user interface, while in unit tests you need to dig in into console errors.

When you start adding accessibility checks for different parts of your system, you may encounter many violations at first. It is better to still add tests, that ignore known violations, and then incrementally fix the issues. This approach prevents regressions, while delaying adding test until all violations are fixed may cause introducing new ones while fixing others.

Testing focus in JavaScript

This blog post is an overview of testing focus behavior in web browser.

During the work on Azure Portal I spent quite a bit of time on ensuring rich keyboard support. This requires appropriate focus management. When user press some keyboard shortcut, the focus should move to appropriate element. There is a good article on MDN about Keyboard-navigable JavaScript widgets. Focus behavior should be also tested very succinctly. As it is very easy to change (break) with even the smallest change in the HTML or JavaScript.

Standard test goes as follows:

  • Arrange: open some page
  • Act: execute some keyboard shortcut that should open particular page and/or set focus on particular element
  • Assert: check if expected element is focused

How to check if element is focused

The simplest way is to use jQuery:


However this may not always work. Especially if you run your unit tests in parallel, because $element.is(‘:focus’) will not work when window does not have focus.

The better (right) way is to use document.activeElement:


This will work even when browser window is not focused.

Testing async actions

Sometimes, keyboard invoke asynchronous actions that eventually will change focus. This can cause:

  • false negative tests: assertion was executed before focus was eventually set
  • false positives: finally focused element, got focus after assertion was executed

The simplest recipe for the first problem is to delay assertion:

setTimeout(() =&gt; {
}, 100);

The problem with this approach is choosing appropriate delay for assertion. Therefore it is better to avoid raw setTimeout, and use polling approach that I described in my post setTimeout considered harmful:

    () =&gt; document.activeElement === element, 
    () =&gt; {
    () =&gt; {

The polling function can be also used for the second solution (by changing assertion order in callback functions). However, for the false positives problem, simple setTimeout is good enough, because we do not have a choice other than wait some particular period of time to execute assertion.

Invoking keyboard actions

There are 3 types of events that we can use to simulate keyboard action:

  • keydown
  • keyup
  • keypress

The safest bet is to use keydown. Why? An example might be using special keys. While in case of keypress – various browsers handle it differently (e.g., by not triggering the event), keydown is pretty consistent. I recommend you to check this article if you are interested in details. It was not updated for some time, but it will give you an idea.

In order to detect keyboard actions you may handle events on capture or bubbling phase. You should choose model depending on your needs, but in general bubbling phase is optimal solution. Additionally it is supported by jQuery, with browser inconsistencies taken care of for you.

To invoke keydown event in your tests, you need to set focus on the element first:

  .trigger("keydown", { which: keyCode });

You can find JavaScript key codes here.


Use document.activeElement to check which element is focused.
Use polling approach for testing async actions.
Use keydown event, and bubble phase to invoke/handle keyboard actions.

Seattle Code Camp: Aurelia and TDD with TypeScript, AngularJS, and Node.js

Last Saturday I had a pleasure to speak at Seattle Code Camp. It was an amazing event, which was free. There were over 50 talks, 500 attendees, and raffle with many prizes, e.g., Microsoft Surface Pro 3!

Seattle Code Camp - Aurelia

Aurelia – the Next Generation JavaScript Framework you will love

Aurelia is a next generation JavaScript client framework that leverages simple conventions to empower your creativity created by Rob Eisenberg, creator of Durandal, who left Angular 2 team to create cleaner and simpler JavaScript framework of tomorrow written in ECMAScript 7!

In this talk I am showing how to get started with Aurelia, and how ES7 (aka ES 2016), JSPM, System.js, babel, and gulp can make you development amazingly fast, smooth, and enjoyable.




You can find demo app I created during presentation on github.

TDD with TypeScript, AngularJS, and Node.js

TypeScript helps to develop and maintain large web applications. Strong typing prevents from introducing bugs, but it doesn’t mean we can give up on testing. In this talk I showed how we can use TDD for building web applications with TypeScript on the client side (with AngularJS) and server side (with NodeJS). I showed a few JavaScript testing frameworks (mocha, Jasmine), and showed a few tools that can make Web Developer’s life easier (npm, gulp, bower, tsd, karma, protractor).




You can find demo app I created during presentation on github.

More is coming

I will be speaking about Aurelia, and TDD with TypeScript, AngularJS, and Node.js at various events this fall. You can find more details in my speaking page.

Regular Expression Translator

Another class I am taking this semester (except Real-Time Systems which I blogged about) is Formal Language Theory. It is very theoretical course. Most of the time is spend on formal proofs. Fortunately, one programming assignment was very fun.

The goal was to implement the program, which checks if one regular expression is subset of another. Thus, the input is two regular expressions.

RegEx AutomatasThe program use basic regular expressions notation and supports following operators:

  • + (union)
  • * (Kleene closure)
  • ε (Epsilon, empty expression)
  • 0,1,2 (literals)

To solve the problem, I had to take advantage of finite automatas (ε-NFA and DFA) in following order:

  1. Parse regular expressions E1 and E2
  2. Create ε-NFAs N1 and N2 using Visitor pattern and transition described here
  3. Convert ε-NFAs N1 and N2 to DFAs D1 and D2 based on this
  4. Create D’I DFA, which is intersection of D1 and D2 DFAs generated in step 3

Implementation details


  • Eclipse
  • Scala
  • Java
  • ANTLRWorks 2
  • Scala JUnit tests

I took advantage of ANTLR for parsing. I want to learn Scala and I am using it for every programming assignment in this semester if possible. ANTLRWorks 2 does not support Scala (it does not generate parser/lexer/visitor in Scala). However, ANTLRWorks 2 generates Java and interoperability between Scala and Java is easy. I decided to try it!

Scala is a main language in which this application was developed. ANTLRWorks 2 was used for parsing regular expression. The new version (v.2) generates Visitor class, which enables iterating through AST (Abstract Syntax Tree) nodes and perform appropriate actions. As I mentioned, ANTLRWorks 2 does not generate Scala code yet. Thus the generated parser and Visitor is in Java language.

During the intersection of DFAs creation, there is an exception thrown in 2 cases:

  • There exists some node of newly created D’I DFA, which is sum of D1 final node and D2 not final node
  • Some transition, which exists in D1 leads to dead node in D2

Exception contains string, which is accepted by L(E1), but not by L(E2). Then, this string is returned as a result of execution. If no exception was thrown, it means, every final state of D1 is also final state of D2. That means L(E1) ∈ L(E2) and ‘true’ is returned.

Running program

The main program is Main.scala. You can find there String variables defined with sample Regular Expressions. The easiest way is to replace them (if you want to test different ones). You can also read input from the console (by commenting and uncommenting appropriate lines).

Empty regular exception cause Exception throw.

There is also set of unit tests to test some regular expressions. You are more than welcome to add new Unit tests if you want to.


Every closure has to have parenthesis: (exp)*
Union also require parenthesis and multiple unions are allowed: (exp1+exp2+exp3)
Sample inputs:

  • (0+1+2)*
  • ((0(0+2)*+1)*+2)
  • ((0(0+2)*+1)*+2+12+(00+21)*+0000110102)

Details about accepted input can be found in ANTLR grammar file.


In this assignment I was able to reuse my knowledge about compilers, learnt last semester in Compilers course I had. Additionally I had to implement automata representation and apply recursion to accomplish required tasks.

It is very simple translator. Handle only basic regular expressions and small language (only 0,1,2 literals allowed). However, the goal was to practice and understand how Regular Expressions work internally.

You can check the code of my translator on github: RegExpTranslator.