Test Driven Development: A Love Story

A Love Story

@nellshamrell

Test Driven Development

Tuesday, April 16, 13

Code


Legacy Code





Grief


Stages of GriefDenialAnger

BargainingDepressionAcceptance


Grief


Test Driven Development is the key

TDD



Denial


I will write tests when I have time


Changed Class


Changed Class

Unrelated Class

Unrelated Class


Changed Class

Unrelated Class

Unrelated Class

Unrelated Class


Changed Class

Unrelated Class

Unrelated Class

Unrelated Class

Unrelated Class

Unrelated Class

Unrelated Class

Unrelated Class

Unrelated Class

Unrelated Class

Unrelated Class


Deploying without tests is flying blind


A magical, better time in the future never comes


The more stress you feel, the less testing

you will do...- Kent Beck


The less testing you do, the more errors

you will make- Kent Beck


The ideal time to write tests is now


But...where do I start?



Anger


What were they thinking?!


I cannot change past actions


I can only change my own actions


Adding tests to legacy code takes time


Take small steps that can be verified

- Noel Rappin


Any new code must have tests


New Code

Legacy Code

Call new testedcode from legacy

code


Bugs in code must be reproduced with a test


User Steps Test Steps


User Steps Test StepsVisit form



Leave field blank



Leave field blank

Click “Submit”



Leave field blank

Click “Submit”

Application crashes



Leave field blank

Click “Submit”

Application crashes

New object



Leave field blank

Click “Submit”

Application crashes

New object

Leave field blank



Leave field blank

Click “Submit”

Application crashes

New object

Leave field blank

Save object



Leave field blank

Click “Submit”

Application crashes

New object

Leave field blank

Save object

Test returns exception


What should my code do?


it “returns a useful error” do

end



end

new_object = Object.new



end

new_object = Object.newnew_object.required = nil



end

new_object = Object.newnew_object.required = nilnew_object.save!



end

new_object = Object.newnew_object.required = nilnew_object.save!new_object.errors.should include (“Required field is blank”)


Use tests to learn legacy code



Bargaining


I write my code, then write my test


Write Code

Write Tests


Write Code


Write Code

Manually Test


Write Code

Manually Test

Modify Code


Write Code

Manually Test

Modify Code

Manually Test


Write Code

Manually Test

Modify Code

Manually Test

WriteTest


Write Code

Manually Test

Modify Code

Manually Test

WriteTest

Modify Code


Write Code

Manually Test

Modify Code

Manually Test

WriteTest

Modify Code

Manually Test


Write Code

Manually Test

Modify Code

Manually Test

WriteTest

Modify Code

Manually Test

ModifyTest


Testing last leaves holes in test coverage


Write FailingTest


Write FailingTest

Make Test Pass


Write FailingTest

Make Test Pass

Refactor


Write FailingTest

Make Test Pass

Refactor

Red


Write FailingTest

Make Test Pass

Refactor

Red Green


Write FailingTest

Make Test Pass

Refactor

Red Green Refactor


Never write new functionality without

a failing test- Steve Freeman

& Nat PryceTuesday, April 16, 13

Testing is about trust

- Robert C. Martin



Depression


What’s the point?


Change will happen


Every line of tested code is reliable code


Every line of untested code is unreliable code


Do the right thing



Acceptance


Tests prevent breaking


Tests are documentation


it “returns the correct rate” do tax_rate(seattle).should == .095end


it “returns the correct rate” do tax_rate(seattle).should == .095endit “creates a new object” do get :new assigns(new_object).should_be new_recordend


it “returns the correct rate” do tax_rate(seattle).should == .095endit “creates a new object” do get :new assigns(new_object).should_be new_recordendit “saves to the database” do expect(save_method).to change{Table.count}.by(1)end


Test Driven Code is better code


ModularLoosely CoupledSmall Methods

Test Driven Code is...


Tests remove fear



Love


Test Drive an external API?


My Code API


My Code API

Calls API method


My Code API

Calls API method

Sends response


Mocks and Stubs


A stub is a stand in for an object called

by my code


My Code API Stub


My Code

Calls API method

API Stub


My Code

Calls API method

Sends scripted response

API Stub


Mocks are “stubs with attitude”

- Russ Olsen


My Code API Mock


My Code

Calls API method

API Mock


My Code

Calls API method

Sends scripted response

API Mock


My Code API Mock


My Code

Unexpected method call

API Mock


My Code

Unexpected method call

API Mock

Test FAILSX


The truth is out there(Just need to ask!)


Testing is evolving


Testing is a journey


Test Driven Development changed my code


Test Driven Development changed me


Test Driven Development is developing

beyond myself


Code


Nell Shamrell

Software Development Engineer withBlue Box Inc

@nellshamrellTuesday, April 16, 13

Documents

Test Driven Development: A Love Story