Testing Your Contracts - Truffle Documentation [1 min read]
This short section from the Truffle Docs explains a little about the testing process and how it fits into the overall Truffle development process.
Writing tests in Solidity - Truffle Documentation [4 min read]
If at this point you are in love with Solidity (as you should be), and want to write your units tests in it too, Truffle offers support to do this as well. This is extremely useful because you can test how smart contracts will interact with each other instead of just with Web3.
Testing for Throws in Truffle Solidity Tests - Simon de La Rouviere, Truffle Tutorials [5 min read]
This tutorial from Truffle shows how to use test for throws within smart contract execution.