The official repository of Elgg is located in https:/github.com/Elgg/Elgg

Personal copies of the official repository are called forks. You can test branches in someone else's fork by adding it as a new remote of your local repository.

Let's add the fork https://github.com/juho-jaakkola/Elgg as a new remote. Go to your Elgg directory and give the command:

git remote add juho-jaakkola https://github.com/juho-jaakkola/Elgg.git

Now when you give the fetch command it fetches the changes both from the official repo and all the other remotes:

git fetch

After this you can checkout branches that haven't yet been merged into the official repo but are still waiting for a review as a pull request.

git checkout -b pr_1234 juho-jaakkola/pr_1234

Now you have a local branch "pr_1234" that is an identical copy of Juho's branch, and you can test the changes introduced in the pull request!