Python E-Commerce Demo#

In this example you will learn how to model your e-commerce website as a directional graph, how to use actions, guards and shared state in your graph model. You will learn how to use AltWalker’s online, offline, walk, check and verify commands.

The tests are written in python with Selenium and PyPOM (Python Page Object Model). You can find the tests source code here.

The e-commerce website being tested is written in markdown and uses Jekyll to generate static files. For cart and order management it uses Snipcart. The website is hosted on GitHub Pages and its forked from Snipcart on GitHub.

Page Object Pattern#

Page Object is a Design Pattern which has become popular in test automation for enhancing test maintenance and reducing code duplication. A page object is an object-oriented class that serves as an interface to a page of your AUT. […] The benefit is that if the UI changes for the page, the tests themselves don’t need to change, only the code within the page object needs to change.

Selenium | Page object models

Model-Based Testing with Page Object Pattern#

When you are using Model-Based Testing with Page Object Pattern:

  • the Page Object Pattern separates your test code from the specific code that interacts with the AUT

  • the Model-Based Tests separates your test code from the flow of the AUT by abstracting the flow in the models.

Now if the UI changes you will only need to update the Page Objects and all the flows (from the model) will reflect the new changes. And if the flow changes you will only need to add new element to your model.


For this Demo we used geckodriver to launch the Firefox browser.

  • Download geckodriver. After you download and extract the executable, make sure you set the path to the geckodriver executable in the Path variable to make other programs aware of its location.

> set PATH=%PATH%;C:\bin\geckodriver
$  ln -s /path/to/geckodriver /urs/local/bin/geckodriver
  • Clone the examples repository:

$ git clone
$ git clone
  • Go into the e-commerce demo directory:

$ cd altwalker-examples/python-ecommerce
  • (Optional) Create a python virtual environment:

> python3 -m venv .virtualenv
> .virtualenv\Scripts\activate
$ python3 -m venv .virtualenv
$ source .virtualenv/bin/activate
  • Install the python dependencies:

$ pip install -r requirements.txt


$ python3 -m pip install -r requirements.txt


We have modeled our e-commerce website as two graphs connected by two shared states. One of the models handles the navigation process of selecting a product and adding it to the cart and the other model handles the checkout process.

Each vertex in the graph represents a state (e.g. v_cart_not_empty). This is where we put our asserts.

Each edge in the graph represents an action (e.g. e_add_to_cart, e_go_to_product_page). This is where we put our page interaction code.


Screenshot of the models taken from the Model-Editor.#

The models/navigation.json contains NavigationModel and the models/checkout.json CheckoutModel:

  • NavigationModel contains edges and vertices that verify homepage and product page behavior.


Screenshot of the NavigationModel taken from the Model-Editor.#

  • CheckoutModel contains edges and vertices that verify the checkout process.


Screenshot of the CheckoutModel taken from the Model-Editor.#

Shared States#

NavigationModel and CheckoutModel are linked together by two shared states:

  • cart-open: The v_cart_open_and_not_empty from NavigationModel is linked with v_cart_open_and_not_empty from CheckoutModel.

  • homepage: The v_homepage from NavigationModel is linked with v_homepage from CheckoutModel.


To link to vertices from two models they need the have the same shared state value, the name of the vertices doesn’t have to be the same.

If GraphWalker reaches v_cart_open_and_not_empty from NavigationModel model, it will continue on v_cart_open_and_not_empty in CheckoutModel, and if reaches v_hompage from CheckoutModel it will continue on with v_homplage from NavigationModel.

Separating the model in two smaller models it makes the model and the code more maintainable. This makes also easy to run tests with only one model that test just a behavior.

Modelling is development work just like coding. Use normal coding good practices like will make your life easier later.

Actions and Guards#

The global.itemsInCart variable is initialized at start in NavigationModel’s actions:

    "actions": [
        "global.itemsInCart = 0;"

The actions from the model level will be executed before any element from the model.

And its value is updated in add_to_cart_from_homepage, add_to_cart_from_product_page and e_place_order, where it’s increased by one each time one of the three edges is reached:

    "actions": [

The cart_open_and_not_empty vertex from NavigationModel* has 4 edges linked into it. All of the 4 edges are guarded by:

    "guard": "global.itemsInCart > 0"

That means that GraphWalker will not generate a path that goes through the guarded edges unless global.itemsInCart is greater than 0.

This way we make sure that every time we reach cart_open_and_not_empty we have items in cart and we can jump to CheckoutModel.


The tests can be found inside tests package.

We use Selenium and PyPOM (Python Page Object Model) to interact with the e-commerce website. The code that interacts with the page, is inside tests/pages/ package.

Each model defined in models/default.json has an associated class in tests/ The models/default.json contains two models: NavigationModel and CheckoutModel, so test/ contains two classes named after each model: NavigationModel and CheckoutModel.

Each model class has a method for each edge and vertex from the corresponding model.

During execution of tests, whenever the path reaches the vertex with the id v_homepage defined in the NavigationModel model, AltWalker will execute the method: tests/



Inside tests/page/ we define our Page Object Model for the home and product pages.

Inside tests/ we define our test code for our model(s).


We use the setUpRun and tearDown fixtures to manage Selenium’s WebDriver session.

Inside the setUpRun function we create the selenium driver:

def setUpRun():
    # ...

    print("Create a new Firefox session")
    driver = webdriver.Firefox(options=options)

    # ...

And in the tearDownRun we close the driver:

def tearDownRun():
    # ...

    print("Close the Firefox session")

Checking the Models#

$ altwalker check -m models/navigation.json "random(edge_coverage(100))"

Checks the integrity of the model(s).

You can also check multiple models this will also check that all models can be reached.

$ altwalker check -m models/navigation.json "random(edge_coverage(100))"  -m models/checkout.json "random(vertex_coverage(100))"

Verifying the Code#

$ altwalker verify -m models/navigation.json tests

Verifies that your model and tests are valid, and that all names referred in the model are implemented in tests package.

Running the Tests#

AltWalker provides two ways of running the tests:

  • Online Mode (On the fly)

    Generate one step at a time and execute it.

  • Offline Mode

    Generate a list of steps which can be executed later.

Online Mode#

$ altwalker online -m models/navigation.json "quick_random(edge_coverage(100))" tests

Walks randomly through the graph until all edges have been passed.

You can also run tests with two models.

$ altwalker online -m models/navigation.json "random(edge_coverage(100))" -m models/checkout.json "random(edge_coverage(100))" tests

Offline Mode#

$ altwalker offline -m models/navigation.json "random(length(15))" -f steps.json

Generates a valid path through the test graph and saves the list of steps into steps.json.


The offline command doesn’t run the tests it only generates a path.

$ altwalker walk tests ./steps.json

Executes (walks on) the steps from the steps.json file.