Антипаттерны модульного тестирования

Антипаттерны

модульного тестирования

Митин Павел, RubyConfUa 2010

О себе

• Ruby on Rails разработчик

• 4 года практики в стиле test-driven development

• http://novembermeeting.blogspot.com

Indented test code vs Правило Шапокляк

describe PopularityCalculator, '#popular?' do it 'should take into account \ the comment count' do subject.popular?(post).should be_false end

# ...end


class PopularityCalculator def popular?(post) endend


it 'should take into account the comment count' do posts = (0..19).map do |n| post_with_comment_count n end

posts.each do |post| if 10 < post.comment_count subject.popular?(post).should be_true else subject.popular?(post).should be_false end endend


class PopularityCalculator THRESHOLD = 10

def popular?(post) THRESHOLD < post.comment_count endend


it 'should take into account the comment count' do posts = (0..19).map do |n| post_with_comment_count n end

posts.each do |post| if 10 < post.comment_count subject.popular?(post).should be_true else subject.popular?(post).should be_false end endend


Мотивация:

• борьба с дублированием

• работы с неконтролируемыми аспектами системы(время, дисковое пространство и т.д.)


Правило Шапокляк: Это хорошо ... хорошо, что Вы зеленый и плоский


it "should return true if the comment count / is more then the popularity threshold" do

post = post_with_comment_count THRESHOLD + 1 subject.popular?(post).should be_true

post = post_with_comment_count THRESHOLD + 100 subject.popular?(post).should be_true end


Бенефиты:

• тесты проще понять

• тесты содержат меньше ошибок

Production Logic in Test

class PopularityCalculator THRESHOLD = 10

def popular?(post) THRESHOLD < post.comment_count end end


it "should take into account the comment count" do post = post_with_comment_count 11 expected = THRESHOLD < post.comment_count actual = subject.popular? post actual.should == expectedend


Мотивация: упростить получение ожидаемого значения


it "should take into account the comment count" do

actual = subject.popular? post_with_comment_count(11)

actual.should be_true

end


Бенефиты: мы действительно тестируем, а не только улучшаем тестовое покрытие :)

Too Many Expectations

describe NotificationService, "#notify_about" do it "should notify the post author by email" do notification_service.notify_about @comment end

it "should notify the post author by sms" end


class NotificationService < Struct.new(:email_service, :sms_service)

def notify_about(comment) end end


before do @email_service, @sms_service = mock, mock @comment = Comment.new 'some text', 'dummy post' @notification_service = NotificationService. new @email_service, @sms_serviceend


it "should notify the post author by email" do

@email_service.expects(:deliver_new_comment_email).

with @comment

@sms_service.expects :deliver_new_comment_sms

@notification_service.notify_about @comment

end Too Many Expectations

it "should notify the post author by sms" do @email_service.expects :deliver_new_comment_email @sms_service.expects(:deliver_new_comment_sms). with @comment @notification_service.notify_about @comment end


def notify_about(comment) email_service.deliver_new_comment_email comment sms_service.deliver_new_comment_sms comment end




with @comment

@sms_service.expects :deliver_new_comment_sms


end

it "should notify the post author by sms" do

@email_service.expects :deliver_new_comment_email

@sms_service.expects(:deliver_new_comment_sms).

with @comment


end


def notify_about(comment) # email_service.deliver_new_comment_email comment sms_service.deliver_new_comment_sms comment end


1)

Mocha::ExpectationError in 'NotificationService#notify_about should notify the post author by email'

not all expectations were satisfied

unsatisfied expectations:

- expected exactly once, not yet invoked: #<Mock:0xb74cdd64>.deliver_new_comment_email(#<Comment:0xb74cdb70>,

#<Mock:0xb74cdf08>)

satisfied expectations:

- expected exactly once, already invoked once: #<Mock:0xb74cde2c>.get(any_parameters)

- expected exactly once, already invoked once: #<Mock:0xb74cdc9c>.author_id(any_parameters)

- expected exactly once, already invoked once: nil.deliver_new_comment_sms(any_parameters)

2)

Mocha::ExpectationError in 'NotificationService#notify_about should notify the post author by sms'

not all expectations were satisfied

unsatisfied expectations:

- expected exactly once, not yet invoked: #<Mock:0xb74c937c>.deliver_new_comment_email(any_parameters)

satisfied expectations:

- expected exactly once, already invoked once: #<Mock:0xb74c9444>.get(any_parameters)

- expected exactly once, already invoked once: #<Mock:0xb74c92b4>.author_id(any_parameters)

- expected exactly once, already invoked once: nil.deliver_new_comment_sms(#<Comment:0xb74c9188>,

#<Mock:0xb74c9520>)


Причины воспроизведения паттерна: отсутствие знаний о стаб-объектах


before do

@sms_service = stub_everything

@email_service = stub_everything

@notification_service = NotificationService. new @email_service, @sms_serviceend




with @comment, @author


end

it "should notify the post author by sms" do

@sms_service.expects(:deliver_new_comment_sms).

with @comment, @author


end


Бенефиты: одна ошибка - один падающий тест

Redundant Fixture

describe PostRepository, "#popular" do it "should return all popular posts" do repository.popular.should include(popular_post) end end

Redundant Fixture

class PostRepository def popular [] end end

Redundant Fixture

it "should return all popular posts" do popular_posts = (1..2).map { build_popular_post } unpopular_posts = (1..3). map { build_unpopular_post } posts = (popular_posts + unpopular_posts).shuffle repository = PostRepository.new posts

actual = repository.popular

actual.should have(2).posts actual.should include(popular_posts.first, popular_posts.last) end

Redundant Fixture

Мотивация: желание получить в тестовом окружении “реальные” данные

Redundant Fixture

VS

Redundant Fixture

before do @popular_post = build_popular_post @unpopular_post = build_unpopular_post @repository = PostRepository.new( [@popular_post, @unpopular_post] )end it "should return a popular post" do @repository.popular.should include(@popular_post) end it "shouldn't return an unpopular post" do @repository.popular. should_not include(@unpopular_post) end

Redundant Fixture

Бенефиты:

• простой setup

• сообщение о падении теста не перегружено лишними данными

• профилактика "медленных" тестов

Neglected Diagnostic vs Ясный красный

describe BullshitProfitCalculator, "#calculate" do it "should return the projected profit" do actual = subject.calculate 'dummy author' actual.should == '$123'.to_money end end

class BullshitProfitCalculator def calculate(author) '$1'.to_money end end


'BullshitProfitCalculator#calculate should return the projected profit' FAILED

expected: #<Money:0xb7447ebc @currency=#<Money::Currency id: usd

priority: 1, iso_code: USD, name: United States Dollar, symbol: $,

subunit: Cent, subunit_to_unit: 100, separator: ., delimiter: ,>,

@cents=12300, @bank=#<Money::VariableExchangeBank:0xb74dabb8

@rates={}, @mutex=#<Mutex:0xb74dab7c>, @rounding_method=nil>>,

got: #<Money:0xb7448038 @currency=#<Money::Currency id: usd

priority: 1, iso_code: USD, name: United States Dollar, symbol: $,

subunit: Cent, subunit_to_unit: 100, separator: ., delimiter: ,>,

@cents=100, @bank=#<Money::VariableExchangeBank:0xb74dabb8 @rates={},

@mutex=#<Mutex:0xb74dab7c>, @rounding_method=nil>> (using ==)


module TestMoneyFormatter def inspect format end end

class Money include TestMoneyFormatter end


'BullshitProfitCalculator#calculate should return the projected profit' FAILED expected: $123.00, got: $1.00 (using ==)


Было: Стало:

красный красный

ясный красный

зеленый зеленый

рефакторинг рефакторинг


Бенефиты: ясное диагностическое сообщение упрощает дальнейшую поддержку теста

Еще антипаттерны

• глобальные фикстуры

• функциональный код, используемый только в тестах

• нарушение изоляции тестов

• зависимости из других слоев приложения

• тестирование кода фреймворка

Антипаттерны в mocking TDD

• мокание методов тестируемого модуля

• мокание объектов-значений

Еще антипаттерны

• “медленные” тесты

• …

Рекомендуемая литература

• Экстремальное программирование. Разработка через тестирование, Кент Бек

• Growing Object-Oriented Software, Guided by Tests by Steve Freeman and Nat Pryce

Исходный код примеров

http://github.com/MitinPavel/test_antipatterns.git


Использованные изображения

• http://dreamworlds.ru/kartinki/27030-otricatelnye-personazhi-v-multfilmakh.html

• http://www.inquisitr.com/39089/former-police-officer-sues-for-discrimination-over-his-alcoholism-disability/

• http://teachpro.ru/source/obz11/Html/der11163.htm

• http://bigpicture.ru/?p=4302

• http://giga.satel.com.ua/index.php?newsid=25654

http://giga.satel.com.ua/index.php?newsid=25654







Спасибо за внимание

RubyConfUa 2010

Антипаттерны модульного тестирования

Documents

sms comment end

post end end

email comment sms

post threshold post

service end

count end end

comment endit

sms end