What are the design principles of software design?

What is the best video that explains principles of object oriented software design methods?

• Answer:

  http://www.eventhelix.com/agile/unit-testing.htm references several videos that guide you through object design principles. These videos from Misko Hevery describe how we can write testable code. They also explain how the act of writing testable code improves the design. This is the foundation of test driven development. The topics covered here are: An Introduction to Unit Testing Global State and Singletons Make the Code Untestable Law of Demeter and Dependency Injection Inheritance, Polymorphism and Testing Psychology of Testing: Tests as Executable Specifications