Automated Unit Testing for Mere Mortals

Jess ChadwickArchitect / RIA Specialist

Dow Jones, Inc

blog.jesschadwick.com@jchadwick

What is an “automated unit test”?

What is a “unit”?

Automated Tests…• Ensure components work as designed• Guard against regressions• Exercise the system• Expose how the system works

– Documentation

Automated Unit Tests are…• Fast• Deterministic• Independent• Repeatable• Focused

Unit tests…• Do not cross application / process boundaries

INTEGRATION TESTS

Integration Tests…• Ensure two or more system components work

together• Cross application / process boundaries

• Are unreliable (non-deterministic)– Encourage ignoring failing tests– This is very bad!

DEMO: A SAMPLE UNIT TEST

TEST DOUBLESMocks and Stubs and Fakes… oh my!

Test Doubles• Stand in for production components• Provide deterministic behavior• Provide control over testing environment

Source: Unit Testing: Exploring The Continuum Of Test Doubles MSDN Magazine, September, 2007

CODE COVERAGE

Code Coverage is…

• The degree to which source code is tested

RETROFITTING EXISTING CODE WITH TESTS

UNIT TEST ANTI-PATTERNS

!! Warning !!

Unit Test Anti-Patterns and Smells

• Test multiple components at once

• Slow– Cross application / process boundaries

• Depend on other tests or external interaction (non-deterministic)

Unit Test Anti-Patterns and Smells

• Multiple assertions

• No assertions

• Unclear / vague assertions

• Logging / Console.WriteLine()

TEST-DRIVEN DEVELOPMENT

A different way of thinking• Part of Agile / Extreme Programming beliefs• Tests drive system design

– TDD = “Test-Driven Design”– “How am I going to test this?”

• Helps create loosely-coupled components

Test-First Development• No code can be written unless driven by a

failing test

• Red – Green - Refactor

TDD Pair Programming Game• Player 1: Write failing test• Player 2: Make failing test pass• Player 1: Refactor• … repeat!

IDEAS TO TAKE HOME

Resources• My Blog: http://blog.jesschadwick.com • Unit Testing Frameworks

– Team System / MS Test– NUnit: http://www.nunit.org

• Visual Studio Add-ins– Test-Driven.Net: http://www.testdriven.net – ReSharper: http://www.jetbrains.com

• Mock Frameworks– Moq, Rhino Mocks, NMock, TypeMock, NUnit

Mocks, DotNetMock, EasyMock.NET