The document discusses various concepts in object-oriented programming and unit testing, including the importance of mocking and dependency injection. It critiques unit testing practices and presents anti-patterns that hinder effective testing. Additionally, it includes examples of Java code illustrating these principles and their implementations.

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Yegor Bugayenko
Object-Oriented JUnit Tests

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Why OOP?

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yegor256/hangman
11
@funivan

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Volume 2
$20
Free shipment

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Unit 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
);
}
}
DependencyInjection

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new Book(new NotRealDatabase());
class NotRealDatabase implements Database {
// ...
}
interfaces
@Override

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static
evil!
singletons
new
interface-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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Hamcrest
An 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 that
the 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 objects
share matchers

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Quality Award.
$4096