Selenium
A mature open project with browser drivers, Grid parallel execution, and Java, Python, C#, and other bindings.
Why use it
Teams with existing test infrastructure reuse it for game sites, dashboards, and web-game shell flows.
Where it fits
Use testing, performance, accessibility, and diagnostic tools to remove problems players will notice.
What to check
Synchronization and driver management are more manual than newer frameworks, and canvas internals still need project test interfaces.