Measuring User Experience with ScalaCheck, Selenium WebDriver, and Six Sigma

I recently stumbled upon an idea that I think can measure defects in user experience, and I want to put it down in writing so I have a starting point for further research.  

The germ of this idea took root in my mind after my last blog post.

In my last blog post, I applied traditional software engineering principles to developing javascript SPAs, and I used automated testing of user stories as an example.

I also happen to have a project where I use scalacheck to automate generative tests for machine learning algorithms and data pipelining architectures.

Further, I happen to have some experience with six sigma from my days working as a defense contractor.

By combining the different disciplines of (a) user story mapping, (b) generative testing, and (c) six sigma, I believe that we can measure the “defects of user experience” inherent in any “system under test”.

Let’s discuss each discipline in turn.

User Story Mapping

User story mapping is an approach to requirements gathering that uses concrete examples of “real world” scenarios to avoid ambiguity.

Each scenario clearly defines the context of the system and how the system should work in a given case, and ideally, describe something that we can easily test with an automated testing framework.

For example, here is a sample “create account” user story

One of the limitations of testing user stories is that they cannot give you a measure of the correctness of your application. This is because to “prove” program correctness with programatic tests we would need to check every single path through our program. 

However, to be fair, the goal of user stories is to gather requirements and provide an “objective” measurement system by which developers, product, and qa can agree to in advance. 

Nevertheless, we still need a means of providing some measure of “program correctness”.

Enter Generative Testing.

Generative Tests

Generative testing tests programs using randomly generated data. This enables you to provide a probabilistic measurements of program correctness. However, this assumes that you know how to setup an experimental design that you can use to measure the accuracy of your program.

For example, the scalacheck documentation provides the following snippet of code that tests the java string class.

If you run scalacheck with StringSpecification as input then scalacheck would randomly generate strings and check whether the properties that you defined in StringSpecification are true.

Here is the result that scalacheck would provide if you ran it with StringSpecification as input.

We can see that scalacheck successfully ran 400 tests against StringSpecification.

Let’s do a little statistical analysis to figure out what this means about our the string class.

According to one view of statistics, every phenomenon has a “true” probability distribution which is really just an abstract mathematical formula, and we use data collection methods to estimate the parameters of the “true” distribution.

We will assume this is the case for this discussion.

Suppose that we do not know anything the String class. Under this assumption, the maximum entropy principle dictates that we assign a 1 to 1 odds to every test that scalacheck runs.

That basically means that we should treat every individual test like a coin flip. This is known as a Bernoulli trial.

Now, some really smart guy named Wassily Hoeffding figured out a formula that we could use to bound the accuracy and precision of an experiment based exclusively on the number of trials. We, unsurprisingly, call it Hoeffding’s inequality.

I will not bother explaining the math. I’m sure that I’d do a horrible job at it.

It would also be boring.

I will instead give a basic breakdown of how the number of trials relate to the accuracy and precision of your experiment.

number of trials margin of error confidence interval
80 10% 95%
115 10% 99%
320 5% 95%
460 5% 99%
2560 2.5% 95%
3680 2.5% 99%
8000 1% 95%
11500 1% 99%

The margin of error measures the accuracy of our experiment and the confidence interval measures the precision of our experiment.

Consider the margin of error as a measurement of the experimental results reliability, and the confidence interval as a measurement of the experimental method’s reliability.

For example, if I had an experiment that used 80 trials and I obtained a point estimate of 50% then this would mean that the “real” value is somewhere between 40% and 60% and that the experiment itself would be correct 95 times out of 100.

In other words, 5% of the time an experiment like this one would generate completely bogus numbers.

Now that I have explained that, let us apply this concept to our StringSpecification object. Based on the fact that we had 400 successful runs we can objectively say that the String class’s “true” accuracy is roughly between 95% – 100%, and that there is only a 1% chance that I am completely wrong.

Easy. Right?

I totally understand if you didn’t understand a single thing of what I just said. Are you still reading?

You might be able to set-up an experimental design and measure the results if you are a statistician. However, it is probably beyond the ability of most people.

It would be nice if there was some general set of methods that we could apply in a cookie cutter way, but still have robust results.

Enter Six Sigma.

Six Sigma

Officially, Six Sigma is a set of techniques and tools for process improvement; so, I do not believe that it is generally applicable to software engineering. However, there are a few six sigma techniques that I think are useful.

For example, we could probably use DPMO to estimate how often out system would create a bad user experience (this is analogous to creating a bad part in a manufacturing process).

DPMO stands for Defects per million opportunities, and it is defined by the formula

Let’s suppose that we decided to use scalacheck to test user stories with randomly generated values.

This would immediately open up the prospect of measuring “user experience” using DPMO.

For example, let’s consider the scenario “Valid Account Information” for the feature “Create Account”.

According to the scenario, there are two things that would make this test fail:

  • not seeing the message “Account Created”
  • not seeing the link to the login screen

Suppose that we ran 200 randomized tests based on this user story, and had 5 instances where we did not see the message “Account Created” and 2 instances where we did not see the link to the login screen.

This means we have 7 defects out of 2 opportunities from 200 samples. Therefore, DMPO = (7 / (200*2)) = 0.0175 * 1,000,000 = 17,500, which implies that if we left our system in its current state then we can expect to see 17,500 defects for every 1,000,000 created accounts.

Notice how much easier the math is compared to the math for pure generative testing.

These are formulas and techniques that an average person could understand and make decisions from.

That is huge.


This is just me thinking out loud and exploring a crazy idea. However, my preliminary research suggests that this is very applicable. I’ve gone through a few other six sigma tools and techniques and the math seems very easy to apply toward the generative testing of user stories.

I did not provide a concrete example of how you would use scalacheck to generatively test user stories because I didn’t want it to distract from the general concept. In a future blog post, I will use an example scenario to walk through a step-by-step process of how it could work in practice.

Stay tuned.

How To Build Testable and Framework Agnostic Single Page Applications with Node.js

In a previous blog post, I spoke about the package principles of cohesion:

  • The Release/Reuse Equivalency Principle
  • The Common Closure Principle
  • The Common Reuse Principle

In this blog post, I will use the principles of package cohesion to build cohesive npm packages, and I will use these npm packages to build testable and framework agnostic single page applications.

For this demonstration, we will create a fake analytics dashboard. Here is what the final product will look like.

Screen Shot 2016-01-31 at 10.14.36 PMGathering Requirements

We will describe the application requirements using the “User Story Mapping” approach.

The following snippet describes the feature of our application

We want our “system under test” to be testable; so, we need to place some architectural restrictions to guarantee “testability”.

At a minimum, a testable system must have the qualities of (a) observability, and (b) controllability.

Observability refers to the property that I can arbitrarily observe the states of the “system under test”, and controllability refers to the property that I can put the “system under test” into an arbitrary state.

The two properties are inherently related to each other: you can’t fully observe a “system under test” that you can’t fully control, and there we don’t care to fully control a “system under test” that we can’t fully observe.

I claim (but will not prove) that these architectural restrictions guarantee “testability”.

In order to support the “controllability” requirement of our architecture, we will use the following background block to load fake data into our “system under test” for every new test run.


By design, a user story will have various scenarios, and we will use the scenarios to determine what needs to be “observable”.

For this demonstration we will consider the following scenarios:

  • Visit the visualization page
  • Change the selected date on the page
  • Aggregate the items by month
  • Aggregate items by year

This snippet shows the scenario description for “visit visualization page”

This snippet shows the scenario description for “change the selected date on the page”:

This snippet shows the scenario description for “aggregate the items by month”:

This snippet shows the scenario description for “aggregate items by year”:

You can see the complete feature file here.

Testing the User Story

The following code snippets uses cucumber.js and babel (an es6 to es5 transpiler) to test the user stories. I use babel because it lets me use generators and coroutines to simplify the asynchronous nature of selenium code.

This snippet initializes the “system under test” based on the data provided in the background block for the user story. This satisfies the “controllability” property of our architecture.

This snippet executes the action(s) that change the state of the “system under test” for the behavior “When I visit the page at <some_url>”:

This snippet executes the action(s) that change the state of the “system under test” for the behavior “When I select the date <some_date>”:

This snippet executes the actions(s) that change the state of the “system under test” for the behavior “When I select to aggregate by <some_aggregation_type>”:

This snippet executes the post conditions checks of the “system under test” for the block “Then I should see a bar chart for <some_title>”.

Note: I will skip the rest of the blocks for brevity’s sake.

In the acceptance tests, I use a page object to encapsulate the data retrieval algorithms for each page.

For example, the following code snippet shows how the page object encapsulates the algorithm that “observes” when the page has finished loading.

This test looks for a DOM element with the html attribute “qa-chart-type”, and then waits for it to change.

We have to do this because the SPA fetches data using a http request when if first loads, and we want to detect when the SPA receives a response.

However, since we cannot easily detect when the SPA receives an http response, we make the SPA communicate this to our test script by creating and updating special “Quality Assurance” html attributes.

This makes testing with selenium much easier and maintainable.

I also created a page object factory to easily change implementations of the page object. It uses the same principles of a “contract test” that I mentioned in my blog post “Contract Tests: or, How I Learned to Stop Worrying and Love the Liskov Substitution Principle”.  

Let’s suppose that we implemented our application using (a) Backbone.js, and (b) React.js.

In order to test a Backbone implementation, we could use the following code

In order to test a React implementation, we could use the following code

This is what running the cucumber application looks like when I test a React implementation:


You can see the complete test suite here

Building Our Components

Suppose that you had the following directory structure for a JAVA application

  • src/
    • use_case001/
      • command/
      • delegate/
      • model/
    • use_case002/
    • use_case003/
    • controller/
    • view/
      • View001.jsp
      • View002.jsp
    • model/

This is an example of a “monolithic” or “big ball of mud” application architecture.

Architects typically have nothing but contempt for this architecture due to its well known rigidity, fragility, immobility, and viscosity.

These are well known application level architectural properties:

  • rigidity measures how easy an architecture can respond to change.
  • fragility measure how likely something will break when making a change
  • mobility measures how easy an architecture can support moving code
  • viscosity measure how easy an architecture supports maintaining the original design

When faced with a monolithic architecture, most architects I know would refactor the monolith into something that looks like this.

  • src/
    • controller/
    • view/
      • View001.jsp
      • View002.jsp
    • model/
  • lib/
    • use_case001.jar
    • use_case002.jar
    • use_case003.jar

Each .jar file is a self contained components that is independently testable, releasable, and versioned.

You might think that simply moving code from a directory to a .jar file does not significantly improve the design. However, when applied properly, it has a huge influence on reducing rigidity, fragility, viscosity, and increasing mobility.

We will use this approach, but in this case we will use npm modules as components: a npm module is equivalent to a JAVA .jar file; so, all the same rules apply.

I will use the discipline of Responsibility Driven Design to guide the cohesion strategy for our components. Responsibility Driven Design makes component “responsibility” the most important organizing principle for code.

I claim (but will not prove) that organizing our components by “responsibility” will force our components to obey (a) the Reuse-Release Equivalency Principle, (b) the Common Closure Principle, and (c) the Common Reuse Principle.

From the scenarios in the user story, I can identify the following responsibilities:

  • Bar Chart Visualization
  • User Interface Interaction
  • Data Retrieval
  • QA HTML Attribute Generation

Therefore, I will respectively create the four following packages:

  • analytics-chart
  • analytics-facade
  • analytics-service
  • qa-locator-utility

Create the “Analytics Chart” Component

The actual details of how I created the component are not important; so, I will not talk about it.

However, I feel that I should mention the unit tests I wrote for the visualizations because it isn’t a common thing.

I created unit tests to prove partial correctness of my application using the approach I describe in my previous blog post.

For example, the following code snippet tests the visualization for some items.

This test verifies that certain DOM elements appear in the svg canvas. I consider it a very weak test because there is a good chance that it could pass and the visualization could still be wrong. However, it is also a cheap test to write; so, there is still value in writing it.

You can see the completed npm package here.

Create the “Analytics Facade” Component

This component encapsulates all the user interface “glue logic” (i.e. identifying which screen or page to display), and we use the command pattern and delegation pattern to promote loose coupling between the user interface and this component.

For example, these are the cucumber features that I wrote for this component.

From a client’s perspective, they only need to know how to execute a command from the facade, and how to delegate tasks to the facade. The cucumber tests above provide a very high level description of what types of commands and delegates this facade exposes.

For the sake of completeness, I will also show you the step definitions for this feature.

You can see the completed npm package here.

Create the “Analytics Service” Component

This component simply makes a request to our remote server and return the json results. It isn’t very interesting; so, I will not discuss it.

You can see the completed npm package here.

Create the “QA Locator Utility” Component

Officially, we do not need this component, but we would like to have an easy method to locate elements in our window’s DOM using xpath. This component encapsulates any algorithms that we might need to simplify the process of creating html attributes for the purpose of writing acceptance tests.

I don’t consider it a very interesting component; so, I will not discuss it. 

You can see the completed npm package here.

Composing the Components Into A Single Page Application Framework

To demonstrate how to migrate the application between frameworks, I will compose the components into (a) Backbone 1.2, and (b) React 0.14.

The following component diagram shows the general relationships between the components and framework.

Screen Shot 2016-02-03 at 11.27.24 PM

Backbone 1.2 and React 0.14

We have placed the bulk of the applications functionality inside of framework independent components. Therefore, in order to create a backbone version or a react version of the application, we have to create a special component that coordinates between our “independent” components and the framework.

In the case of React, we created the component backbone_app.

In the case of Backbone, we create the component react_app.

For example, here is the entry point for our Backbone application:

Here is the entry point for our React application:

The parallels in the code are very apparent. I will not go into detail into the code bases because it is not important. I only care about the “shape” of the design.

You can find the Backbone implementation here, and the React implementation here if you really care to dig into the code, however.


This approach might seem very complicated for such a simple application … and it is.

In reality, this approach only makes sense once your application reaches a certain scale. However, simple applications have a tendency of becoming big applications, and it is very expensive to put a test harness on an already existing system with no tests.

Personally, I recommend you always build an application with decoupled testable components from the very beginning because that investment will pay large dividends in the long run.

Further, decoupling your components from the framework has huge benefits even if you have no intention of switching frameworks.

One practical “use case” is with automated testing.

When you decouple your components from the framework then you can test the bulk of your application independent of the framework. This significantly simplifies the overall testing process.

In fact, the package principles were partially created to minimize the work of creating and maintaining tests.

In a future post, I will show you how you can use a Continuous Integration tool to automatically run your tests whenever someone releases a new version of a component.

That should demonstrate the practicality of strictly following package principles.