An Intro to Test Driven Development (TDD)Rob HaleApril 11, 2016

Goals

• Automated testing isn’t (always) TDD• Where it fits• Moq

Automated Unit Testing

What’s a “unit”

• The test operates in isolation• tests should never depend on each other

Benefits of unit tests over end-to-end tests

• Error localization

• Execution time

• Tighter feedback loop

• Coverage

40x

What’s not a unit test?

I like Michael Feathers’ explanation from Working Effectively with Legacy Code. It’s not a unit test if:

• It talks to a database• It communicates across a network• It touches the file system• You have to do special things to your environment to run it (like

editing a config file)

DIFFICULT SCENARIOS

TO UNIT TEST

Closed Object Models (Sharepoint, Silverlight)

Client – server architecture - Communicating Across a Network

An out-of-process call - Includes talking to databases and Web Services

UI/GUI interactionTouching the File SystemLegacy CodeRequires the Environment to

be configured

Test Driven Development

The basic cycle

Write a failing test

Make the test pass

Refactor

Put another way...

New requirement

Run Tests

Write new test

Write new test

Write new code

Run Tests

Refactor

Make it Better

Make it Fail

Make it Work

“When you first start at doing TDD you know what the design should be. You know what code you want to write. So you write a test that will let you write that bit of code. “When you do this you aren't really doing TDD – since you are writing the code first (even if the code is only in your head ) “It takes some time to realize that you need to focus on the test. Write the test for the behavior you want - then write the minimal code needed to make it pass - then let the design emerge through refactoring. Repeat until done.”

--Brian Rasmussenhttp://www.slideshare.net/baronslideshare/testdriven-development-tdd

An Exercise in Test Driven

Development

The idea here is going to be to go through the exercise of designing a portion of a new solution in real time.

After the exercise I want to circle back and point out the benefits we gained from the test first approach which may have been missed had we coded and then wrote tests.

Principles•Think About What You Are Trying To Do •Follow The TDD Cycle•Never Write New Functionality Without A Failing Test - Each test should be for a single concept

•Continually Make Small, Incremental Changes

•Keep The System Running At All Times - No one can make a change that breaks the system - Failures Must Be Address Immediately

•Is an activity of the developer

• Test code should be treated the same as “production” - maintained - refactor - source control

• Experimentation - Names don’t matter initially

• When you want to change existing code, first write covering, white box, unit tests and then use TDD to add new functionality

• Fix it in the simplest way possible using as many assumptions as you like

TDD gives you

Design

Confidence

Documentation

Feedback

Realizing quality improvement through test driven development

Metric Description IBM:Drivers

MSFT:Windows

MSFT:MSN

MSFT:VS

Defect density of non-TDD team

W X Y Z

Defect density of team using TDD

0.61W 0.38X 0.24Y 0.09Z

% increase in coding time becauseof TDD [Management estimates]

15-20% 25-35% 15% 25-30%

http://research.microsoft.com/en-us/groups/ese/nagappan_tdd.pdf

Visualized another way...

http://research.microsoft.com/en-us/groups/ese/nagappan_tdd.pdf

Moq

What’s a mock object?

A Test Double object that is pre-programmed with expectations which form a specification of the calls they are expected to receive

The nice thing about using mocks while doing TDD is we can mock something that doesn’t actually exist. Just define an interface and mock that. Later on we can create concrete implementations of the interface (through TDD, of course)

Chicago vs London

Ledger

● Calculate(string expression)

Calculator

● Add● Subtract● Multiply● ...

Based on http://programmers.stackexchange.com/a/123672

ledger.Calculate("5 * 7")

[TestFixture]public class LedgerTests{ public static Ledger Ledger { set; get; }

public static int Value { get; set; }

public static Mock<ICalculator> calculator;

[SetUp] public void LedgerSetup() { calculator = new Mock<ICalculator>(); Ledger = new Ledger(calculator.Object); }

Chicago vs London

[Test]public void ChicagoStyle(){ Value = Ledger.Calculate("5 * 7"); Assert.AreEqual(35, Value);}

The Chicago/State school would have you assert whether the result is 35. The jUnit/nUnit frameworks are generally geared towards doing this.

Chicago vs London

[Test]public void ChicagoStyle(){ Value = Ledger.Calculate("5 * 7"); Assert.AreEqual(35, Value);}

The Chicago/State school would have you assert whether the result is 35. The jUnit/nUnit frameworks are generally geared towards doing this.

[Test]public void LondonStyle(){ calculator.Verify(calc => calc.Multiply(5, 7), Times.Exactly(1));}

The London/Interaction school would have you assert whether Calculator.Multiply(5,7) got called. The various mocking frameworks are useful for this, and it can be very useful if, for example, you don't have ownership of the "Calculator" object (suppose it is an external component or service that you cannot test directly, but you do know you have to call in a particular way).

Resources

• http://www.slideshare.net/dehringer/test-driven-development-5785229

• http://www.slideshare.net/baronslideshare/testdriven-development-tdd

• http://research.microsoft.com/en-us/groups/ese/nagappan_tdd.pdf

• http://www.martinfowler.com/articles/mocksArentStubs.html• Video: Llewellyn Falco & Woody Zuill - Practical Refactoring

• https://youtu.be/aWiwDdx_rdo• Video: Raymond Lim & Roy Osherove - TDD Pairing Session 1

• https://youtu.be/xX9hfPkA800• Video: Doc Norton - The Technical Debt Trap

• https://vimeo.com/97507576

Other resources mentioned by attendees

The following resources were mentioned after the presentation. They require purchase or subscription.• Play by Play: TDD with Brad Wilson (Pluralsight)

• https://www.pluralsight.com/courses/play-by-play-wilson-tdd• Automated Testing for Fraidy Cats Like Me with Julie Lerman

(Pluralsight)• https://www.pluralsight.com/courses/automated-testing-fraidy-cats

• Test-Driven Development training by Mike Hill & Joshua Kerievsky (Industrial Logic)

• https://elearning.industriallogic.com/gh/submit?Action=AlbumContentsAction&album=before&devLanguage=Java