cdp-tools offers handy tools for working with Cisco Discovery Protocol (CDP).
cdp-listen/cdp-routemgr are proof-of-concepts that may be beneficial in implementing a similar proposal. Meanwhile, cdp-send is a must-have tool for your situation. It can mimic different kinds of Cisco hardware that you can use for testing the CDP behavior of your network.
However, the source code can be challenging to understand since it is required to build under both old and new versions of libnet. Consequently, it involves a lot of macro-ing.
Moreover, the latest release of cdp-tools includes more documentation in DESCRIPTION and README to help you get started with the software. Overall, cdp-tools is a useful utility for those who work with CDP and Cisco Switches.