Here you have some resources to help in testing and tdd workshops. Hope you will find them useful.
This is the first one, about the basics of Test Driven Development, and the red-green-refactor cycle.
This one about testing value objects:
You can test unpredictable things:
Test doubles and where to find them, with some cute drawings:
Compilation of low-cost techniques to create test doubles without a Doubling Framework:
Enjoy them!