I need to do some research to possibly incorporate DFP into some websites/phonegap apps, and I would like to know if there's a way to be able to test it without actually signing up for DFP and setting up real campaigns and all that.
If there isn't such a thing, what would be the easiest way to test it? I don't really need to learn now anything about running the campaigns, I'm only interested in the integration of DFP with websites/phonegap apps, to test how it works, how it needs to be integrated, etc
You can create a test network if you want to test the API in a separate environment, look at step 3 of https://developers.google.com/doubleclick-publishers/docs/start, just enable the API access and create a Test Network to test your application.