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)
end
end


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
end
end


THRESHOLD = 10

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


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

post = post_with_comment_count THRESHOLD + 100
end


Бенефиты:
• тесты проще понять
• тесты содержат меньше ошибок

Production Logic in Test

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 == expected
end


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_service
end


@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
end


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

@email_service.expects :deliver_new_comment_email
with @comment
end


# 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_service
end


with @comment, @author
end

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

Спасибо за внимание

RubyConfUa 2010

Антипаттерны модульного тестирования

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