Test Automation - Speeding Up Testing with Playwright Python using Local Storage

Introduction

In the world of web application testing, time is of the essence. Slow test execution can drastically hinder the development cycle and delay the delivery of high-quality software. One common bottleneck in testing workflows is the need to simulate user interactions and repeatedly set up specific application states. Fortunately, Playwright offers a powerful solution to address this challenge by leveraging the browser's local storage.

The solution presented in this article is exemplified in my Playwright Python example project, developed in collaboration with Elias Shourosh.

The Problem

Web applications often require users to perform a series of interactions to reach a desired state. During testing, these user interactions need to be simulated, which can be a time-consuming process, especially when dealing with complex application flows or running tests in parallel. For example, testing an e-commerce application may require simulating the process of adding items to a cart, navigating to the checkout page, and filling out various forms. Reproducing these steps for every test can lead to significantly longer run times, slowing down the overall testing process.

Implementing the Solution

The solution code can be found here.

Playwright provides a straightforward way to interact with the browser's localStorage, allowing you to set and retrieve data programmatically. By leveraging this capability, you can streamline your testing workflows and significantly reduce test execution times by skipping redundant user interactions.

Here's an example of how to set a value in localStorage using Playwright Python:

In this code snippet:

1. The @pytest.mark.parametrize decorator is used to set up the browser context with a specific user (in this case, User.STANDARD_USER).
2. Inside the test_checkout_counter test, the page.evaluate method is used to execute JavaScript code within the browser context, setting the value '[4,0]' for the 'cart-contents' key in localStorage. This simulates the state of having two items in the cart, bypassing the need for manual interactions to add items to the cart.
3. After setting the localStorage value, page.reload() is called to refresh the page and ensure the application state is updated based on the new localStorage data.
4. Finally, an assertion is made to verify that the shopping cart badge displays the expected value of "2".

In Conclusion

Playwright's ability to interact with the browser's localStorage provides a powerful tool for optimizing your testing workflows. You can eliminate redundant user interactions by programmatically setting up application states through localStorage, resulting in faster test execution times. This approach enhances testing efficiency and facilitates the creation of more comprehensive and robust test suites, ultimately contributing to the delivery of high-quality software.

Happy testing!