Add tests for integrity values

[greyli]

When the wrong integrity value is used, the CCS/JS file will be blocked. Not sure what's the best way to test it, maybe we could just read the Browser console log to check if it contains info like "Failed to find a valid digest in the 'integrity' attribute for resource".

Ref: https://stackoverflow.com/questions/20907180/getting-console-log-output-from-chrome-with-selenium-python-api-bindings
Related issues:

• Failed to find a valid digest - bootstrap@5.3.2/dist/js/bootstrap.min.js #331
• Fix incorrect JS integrity #332