How to generate network traffic and save it to pcap files?

I want to test *snort*, so I want to have some test network traffic. Since *snort* can read pcap files, I want to generate some traffics which can be customized and save it to pcap files. Here are my questions: 1. Is it right to test *snort* as I said? 2. Is there a good tool to generate traffic and save it to pcap file? Any suggestions about what I going to do means a lot to me!