If you have installed an app from the app store and want to help testing a pull request you can easily apply the changes by using the patch
commandline tool.
Take the pull request URL, append .patch
to it and download the file:
Example for PR: nextcloud/deck#320
wget https://github.com/nextcloud/deck/pull/320.path
Apply the patch to your apps directory:
patch -p1 < 320.patch
Now you can test the changes made by the pull request.
Revert the changes:
patch -p1 -R < 320.patch
This method will only work for changes where there is no build process involved. Some apps use a build process for their javascript code, so changes applyed by the patch will need to go though that first. In those case, installing the app from git might be the easiest way to test a PR.