Object-Oriented JUnit Tests

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Yegor Bugayenko

Object-Oriented JUnit Tests

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Why OOP?

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yegor256/hangman11

@funivan

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Volume 2

$20Free shipment

/38@yegor256 5Unit testing anti-patterns:Happy Path Tests Validation and Boundary Easy Tests The Giant The Cuckoo The Conjoined Twins The Slow Poke Anal Probe Test It All Line Hitter Wait and See The Silent Catcher Chain Gang

The Mockery The Free Ride The Local Hero Wet Floor The Flickering Test The Environmental Vandal Second Class Citizens The Secret Catcher Logic in Tests Code Matching Misleading Tests Not Asserting Asserting on Not-Null

Forty Foot Pole Test With No Name Excessive Setup The Dead Tree The Turing Test The Mother Hen The Sleeper The Butterfly Doppelgänger The Inspector Structured Inspection The Cupcake

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Dependencies

6

are evil

Unbreakable

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class Book { private int id; String title() { return Database.getInstance().fetch( “SELECT title FROM book WHERE id=?”, this.id ); } } String title = new Book().title();

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Book

BookTest

DatabaseSomething

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class Book { private int id; String title() { return DbUtils.fetch( “SELECT title FROM book WHERE id=?”, this.id ); } }

static

Johan Haleby

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class Book { private int id; String title() { return Database.getInstance().fetch( “SELECT title FROM book WHERE id=?”, this.id ); } }

global

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class DbUtils { private static int port; static String fetch(String sql) { // .. } }

class Database { private static Database INSTANCE; private int port; private Database() {} static Database getInstance() { if (Database.INSTANCE == null) { Database.INSTANCE = new Database(); } return Database.INSTANCE; } String fetch(String sql) { // .. } }

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class DbUtils { private static int port; static String fetch(String sql) { // .. } }

class Database { private static Database INSTANCE; private int port; private Database() {} static Database getInstance() { if (Database.INSTANCE == null) { Database.INSTANCE = new Database(); } return Database.INSTANCE; } static void setInstance(Database db) { Database.INSTANCE = db; } String fetch(String sql) { // .. } }

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class Book { private int id; String title() { return new Database().fetch( “SELECT title FROM book WHERE id=?”, this.id ); } }

new

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class Book { private int id; private Database database; Book() { this(new Database()); } Book(Database db) { this.database = db; } String title() { return this.database.fetch( “SELECT title FROM book WHERE id=?”, this.id ); } }

Dependency Injection

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new Book(new NotRealDatabase());

class NotRealDatabase implements Database { // ... }

interfaces

@Override

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static evil!

singletonsnewinterface-less

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Mocking

17

is evil

Ad hoc

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static import org.mockito.Mockito.*; class BookTest { @Test public canFetchTitleFromDatabase() { Database db = mock(Database.class); doReturn(“UML Distilled”).when(db).fetch( “SELECT title FROM book WHERE id=?”, 123 ); Book book = new Book(db, 123); assert book.title().equals(“UML Distilled”); } }

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mocking

algorithm

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Book

BookTest

db

assumptions

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Safety net.(c) By John M, CC BY-SA 2.0

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static import org.mockito.Mockito.*; class BookTest { @Test public canFetchTitleFromDatabase() { Database db = mock(Database.class); doReturn(“UML Distilled”).when(db).fetch( “SELECT title FROM book WHERE id=?”, 123 ); Book book = new Book(db, 123); assert book.title().equals(“UML Distilled”); } }

class Book { private int id; private Database database; Book(Database db, int i) { this.database = db; this.id = i; } String title() { return this.database.fetch( “SELECT title FROM book WHERE id=?”, this.id ); } }

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False positives.

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Fakes or doubles.

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class BookTest { @Test public canFetchTitleFromDatabase() { Book book = new Book( new FakeDatabase(), 123 ); assert book.title().equals(“UML Distilled”); } }

class Book { private int id; private Database database; Book(Database db, int i) { this.database = db; this.id = i; } String title() { return this.database.fetch( “SELECT title FROM book WHERE id=?”, this.id ); } }

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class BookTest { @Test public canFetchTitleFromDatabase() { Book book = new Book( new FakeDatabase() .withTitle(123, “UML Distilled”) .withTitle(1, “Elegant Objects”) .withUser(“Peter Pan”), 123 ); assert book.title().equals(“UML Distilled”); } }

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Ad hoc mocking.

Fakes.

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Algorithms

28

are evil

In-method

Maybe!

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cactoos

www.cactoos.org

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class BookTest { @Test public canBuildURL() { Book book = new Book(); book.setLanguage(Locale.RUSSIAN); book.setEncoding(“UTF-8”); book.setTitle(“Дон Кихот”); assert book.getURL().contains(“%D0%94%”); } }

procedural!

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HamcrestAn anagram for “matchers”.

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A test method must have nothing but a single statement:

assertThat()

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assertThat(book, hasTitle(“UML Distilled”));

“We assert that the book behaves as if it has a title.”

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assertThat( book, hasURL( hasPath( containsString( equalTo(“%D0%94%”) ) ) ) );

We assert thatthe book behaves as if it has a URL that behaves as if it has a path that behaves as if it contains a string that behaves as if it is equal to “%D0%94%”.

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shorter test methods

why?!

immutable objectsshare matchers

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Quality Award.

$4096