Test Driven Development

Why Test Driven Development ?

Pair Programming

Unit Tests

Acceptance Tests

Daily meetings

Iterations

Releases

Agile insists on constant feedback in

all levels

Empirical Feedback

Acceptance test driven development

Write a failing acceptance test

Write a failing

unit test

Make the test pass

Refactor

Regression Test suite

Measure of demonstrable

progress

•Start with Testing a walking skeleton

•A “walking skeleton” is an implementation of the thinnest possible slice of

real functionality that we can automatically build, deploy, and test end-to-end.

Eg., for a database-backed web application, a skeleton would show a flat web page with

fields from the database

•The “end” in “end-to-end” refers to the process, as well as the system

How to start TDD?

How do we write a test ?

Write Tests Backwards

•Write the test name - helps us decide what we want to achieve; •Write the call to the target code - is the entry point for the feature; •Write the expectations and assertions - know what effects the feature should have; •Write the setup and teardown to define the context for the test This sequence reflects how we tend to think through a new unit test. Then we run it and watch it fail.

Object Oriented Programming

A Train Wreck (This is bad because this

one line depends on the interfaces and implied structure of three

different objects.)

dog.getBody().getTail().wag();

Solution: "Tell, Don't Ask”

dog.expressHappiness();

An object should only talk to its

neighbors

Role of Mockobjects

TDD with Mock Objects guides interface design by the services that an object requires, not just those it provides.

System of narrow interfaces each of which defines a role in an interaction between objects,

rather than wide interfaces that describe all the features

provided by a class.

LEAN

Format of TDD using Mockobjects

Create instances of Mock Objects

Set state in the Mock Objects

Set expectations in the Mock Objects

Invoke domain code with Mock Objects as parameters

Verify consistency in the Mock Objects

TDD for distributed teams

"Collective Code Ownership" is critical to distributed agile teams

Continuous Integration should accommodate infrastructure for TDD

You can’t go home with anything that doesn’t build !!