Add integration tests for official plugins

[pantharshit00]

Right now the official abell plugins are not tested at all and it would be great if we can add some integration tests there so that we can build more confidence when we change the renderer code.

I also found that they also lack unit tests per plugin which should also be added but I will value these tests more for now.

Official plugin repo: https://github.com/abelljs/official-plugins

More context: abelljs/abell#77 (comment)

[saurabhdaware]

We can add tests for afterBuild first in https://github.com/abelljs/abell/blob/main/examples/with-plugin/with-plugin.spec.js and test integrations in this same repository.

Later we can unit test the official-plugins repo for the plugin-specific functions.

[saurabhdaware]

abelljs/abell#77 (comment)

Yup this makes sense. Always better to have more tests. Moving this issue to official-plugins repository.