In Test Driven Android Development, we discuss how good Object Oriented Design and Test Driven Design are complementary. We create a simple JUnit test, using a stub object that represents a data feed. Next, we demonstrate how to write a test driven design unit test for a Java class that performs network operations. After that, we create a unit test for a data access object that uses a JSON data feed. Our test includes JUnit 4 asserts and Hamcrest-style asserst. Then, we discuss blockers that prevent us from writing unit tests, and how we can use Mockito, code coverage, and automatic test execution to ameliorate those blockers. Finally, we look at UI testing with Espresso, and multi-platform testing with Firebase.