Tools and procedure for Network testing

Hi all, I just wanted to know how you do your network testing when validating a new design/technology in your Network, especially to ensure that it will meet your SLA requirements for example that a voice call will not be dropped in case of a network element failure ? Do you test with IXIA, multiping, launch somes VM using ping with -i option, Windows ping by setting the timeout interval, or may be directly from the Network device (routers...), Many thanks, Joe