Implement snapshot comparison assertion

[oleiade]

Problem Statement

In a recent internal discussion the potential need to be able to compare browser modules screenshot arise.

Users would like to have the ability to easily compare two screenshots taken by the browser module (unclear if this is prior, or during the test), and assert whether they are different or not.

As it turns out Playwright's assertion framework has matchers dedicated to that, namely toHaveScreenshot and toMatchScreenshot. See their Visual comparison guide, and Snapshot Assertions reference for more detail.

The general idea behind those matchers is to compare the result of a screenshot operation with a pre-existing image, or both pre-existing screenshots, to determine a level of similarity between them, and assert on it, based on acceptable difference parameters and controllable thresholds.

Under the hood, Playwright appears to be using Mapbox's pixelmatch library to perform comparisons.

Solution(s)

To be decided.