Test Driven Development

Test Driven Developme

nt

Technique to design and develop software.

Practice part of the Extreme Programming methodology — XP

Based on three fundamental pillars.

The Three Pillars

Implement the exact functionality of the software.

Reduce the number of defects on the software – good quality software

Produce modular and highly reusable software.

When Doing TDD

It’s not about just writing tests.

Translate use cases to examples. Enough to describe the functionality without ambiguity.

Architecture will eventually emerge.

The TDD Algorithm

Red

GreenRefactor

The TDD Algorithm

Red

GreenRefactor

TDD In ActionWith an example ;-)

The Problem

Email validation mechanism

The Problem

Email validation mechanism

?

The Problem

Email validation mechanism

Neither empty nor null.

Has to contain an @ symbol

Has to belong to the .com, .net and .edu TDLs

Domain part can’t be 1 character long

All lowercase

Not contain numbers

Only _ . - symbols

Before we begin

Writing Tests

Testing framework Part of the language

Ruby Rust Go Python

External tools and libraries

Neither empty nor null

Red@Testpublic void shouldReturnFalseIfEmailIsNull() { String email = null; EmailValidator validator = new EmailValidator();

boolean isValid = validator.isValid(email);

assertThat(isValid, equalTo(false));}

Neither empty nor null

Green public boolean isValid(String email) { return false;}

Neither empty nor null

Red

@Testpublic void shouldReturnTrueIfEmailLengthIsGreaterThanZero() { String email = "some@email.com"; EmailValidator validator = new EmailValidator();

boolean isValid = validator.isValid(email);

assertThat(isValid, equalTo(true));}

Neither empty nor null

Greenpublic boolean isValid(String email) { if (email == null) { return false; } return email.length() > 0;}

Contains an @ symbol

Red

@Testpublic void shouldReturnFalseIfEmailDoesntContainAtSymbol () { String email = "someemail.com"; EmailValidator validator = new EmailValidator();

boolean isValid = validator.isValid(email);

assertThat(isValid, equalTo(false));}

Neither empty nor null

Greenpublic boolean isValid(String email) { if (email == null) { return false; } if (!email.contains("@")) { return false; } return email.length() > 0;}

Refactorprivate EmailValidator validator;

@Beforepublic void setUp () { validator = new EmailValidator();}

In the end… Components will behave exactly as we want.

Tests will be the documentation of our system.

Tests will break if changes compromise the system.

Thank you!Carlos Andrés Oquendo

coquendo@thoughtworks.com@andres19_05