3 Elements of TDD

Todd Wei

Outline Overview of TDD Test First Development Iterative Incremental Development Refactor

TDD

Pass the test case

RefactorWrite a

failing test case

3 Elements of TDD

TFD

IIDRefactor

Outline Overview of TDD Test First Development Iterative Incremental Development Refactor

Test First Development

Write a Failing Test Case

Pass the Test Case

Why Write Test First? Testability Code Coverage Quick Feedback Simple Design Decoupling Bug Free …

?

Decoupling

Testability

Coverage

Why Write Test First? Testability Code Coverage Quick Feedback Simple Design Decoupling Bug Free …

Specification

Decoupling

Testability

Coverage

Test Case as Specification

“Specification by Example”–Martin Fowler

What’s Specification?

“A specification is an explicit set of requirements to be satisfied by a material, product, or service.” -- Wikipedia

What’s Specification?

User Vendor

Specification

Specification is in Every Level

Where does specification come from?

Requirement

Specification

Requirement Analysis

Test Case as Specification

Requirement

Document

Requirement

Test Case

Traditional

TDD

Software Specification Forms

Specificatio

n

DocumentDesign by ContractTest Case

Document

General

Not Precise

No Feedback

Not Reliable

Design by Contract Contract

Precondition Postcondition Invariant

Precise

Quick Feedback

Abstraction

Limited Functionality

Test Case

Precise

Quick Feedback

User Friendly

Not General

How to Write Good Test Case

Follow requirements

Think of as black box

Construct a scenario

Verify external behavior

Example: Stack

FILO

Bad Test Style

push()

data

pop()

Function/procedure/method and data are the focuses of test

Bad Test Style

Good Test Style

push()

data

pop()

Stack

Feature is the focus of test, e.g. FILO

Good Test Style

Bad vs Good

Bad Good

Behavior

Scenario

Black Box

Requirement

State

Procedure

White Box

Implementation

4 Steps on Writing Good Test Case

Follow requirements

Think of as black box

Construct a scenario

Verify external behavior

Outline Overview of TDD Test First Development Iterative Incremental Development Refactor

Iterative Incremental Development

Pass the test case

Write a failing test

case

TDD = TFD + IID + Refactor

Waterfall

Requirement Analysis

Design

Implementation

TestMaintenance

Waterfall

Phase1

Phase2

Phase3 …

Layer Hierarchy

Business Logic Layer

Presentation Layer

Data Access Layer

Agile: Iterative Incremental Development

Feature1

Feature2

Feature3

…

Feature1.1

Feature1.2

Feature1.3

…

Feature Hierarchy

Example: multi-dimensional objectName Project Expertise Degree Gender

Allen Project1 Develop Master Male

Rebecca Project1 Test Bachelor Female

Kay Project2 Develop Bachelor Female

David Project2 Test Master Male

… … … … …

Company

Develop

Project1

Project2

Test

…

Company

Project1

Develop Test

Project2

…

Function Cohesion

“Parts of a module are grouped because they all contribute to a single well-defined task of the module” -- Wikipedia

What does unit mean?

Unit vs Atom

What does unit mean?

Hierarchy vs Single Responsibility

What should be tested in unit test?

Do unit test on all levels that can be automated!

Outline Overview of TDD Test First Development Iterative Incremental Development Refactor

TDD

Pass the test case

RefactorWrite a

failing test case

TDD = TFD + IID + Refactor

Software Entropy

Software complexity, change cost increase exponentially as the project goes on

Chaos is not agile

Refactor

Refactoring is a disciplined technique for altering its internal structure without changing its external behavior

Refactor: Bring Order to Chaos

Refactor with TFD

TFD facilitates refactoring and ensure no functionality is broken with regression tests

Refactor with IID

Version1

Version1.1

Version2

Refactor to a stable intermediate version before adding new feature

Summary

Pass the test

case

Refactor

Write a failing test case

TFD

IIDRefactor

Question & Answer

Thanks!