Continuous Integration using composer

One way to speed it up is to use composer install --prefer-dist which only downloads zips even for dev packages. This is preferred for unique builds since it skips the whole history of the project.

As for sparing packagist, don't worry about it too much, one build every hour isn't going to make a huge difference compared to all the open source libs that build on travis at every commit.

One thing you could do is to store vendors in a location outside of project's workspace in jenkins so that it remains between the builds. You not necessarily need to change your application. Just update the build script so that it creates a symbolic link to the vendors location.

I use capifony for deployment and it uses this approach to keep the vendors between releases.

One thing to note is that Composer caches packages that it downloads. So once they are downloaded the first time, they should work even if Packagist is down (not 100% sure), and network bandwidth spared (100% sure).

Second thing is: why are you running tests by doing a fresh checkout of the repository? It is entirely possible to keep a copy of your code in the workspace in Jenkins, and just make sure you wipe on every test run the caches, logs and other artifacts. This will speed up not only composer install, but also the git pulls, especially for big repos!

Side note: for our own Jenkins platform, where workspaces are not cleaned between tests, the main drawback we found with composer is the sheer amount of disk space taken by having the full vendor dir in each workspace. I tried to work around this by using symlinks and sharing the vendors (named based on hashes of composer.lock), but then composer autoloader had a bit of problems finding where to load classes from...