How difficult is to automatically test the HelloWorld. We fix it and other many difficult scenarios with techniques like: - lower "s" singleton - law of demeter - dependency injection - and more examples

1. 05 BARCELONA
David Rodenas, PhD
TDD Course
IMPROVE TESTING

2. @drpicox
HELLO WORLD
IMPROVE TESTING 2

3. @drpicox
@drpicox
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
HELLO WORLD
3
IMPROVE TESTING — HELLO WORLD

4. @drpicox
@drpicox
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
@Test
public void say_hello_world() {
HelloWorld.main(null);
assertThat(???)
}
HELLO WORLD
4
IMPROVE TESTING — HELLO WORLD

5. @drpicox
@drpicox
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
@Test
public void say_hello_world() {
var buffer = new ByteArrayOutputStream();
var out = new PrintStream(buffer);
System.setOut(out);
HelloWorld.main(null);
assertThat(buffer.toString()).isEqualTo("Hello Worldn");
}
HELLO WORLD
5
IMPROVE TESTING — HELLO WORLD

6. @drpicox
@drpicox
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
@Test
public void say_hello_world() {
var realOut = System.out;
var buffer = new ByteArrayOutputStream();
var testOut = new PrintStream(buffer);
System.setOut(testOut);
HelloWorld.main(null);
System.setOut(realOut);
assertThat(buffer.toString()).isEqualTo("Hello Worldn");
}
HELLO WORLD
6
IMPROVE TESTING — HELLO WORLD

7. @drpicox
@drpicox
public class HelloWorld {
private PrintStream out;
public HelloWorld(PrintStream out) {
this.out = out;
}
public void sayHello() {
this.out.println("Hello World");
}
public static void main(String[] args) {
new HelloWorld(System.out).sayHello();
}
}
HELLO WORLD
7
IMPROVE TESTING — HELLO WORLD

8. @drpicox
@drpicox
@Test
public void say_hello_world() {
var buffer = new ByteArrayOutputStream();
var testOut = new PrintStream(buffer);
new HelloWorld(testOut).sayHello();
assertThat(buffer.toString()).isEqualTo("Hello Worldn");
}
HELLO WORLD
8
IMPROVE TESTING — HELLO WORLD

9. @drpicox
@drpicox
HELLO WORLD
9
IMPROVE TESTING — HELLO WORLD
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
@Test
public void say_hello_world() {
var buffer = new ByteArrayOutputStream();
var out = new PrintStream(buffer);
System.setOut(out);
HelloWorld.main(null);
assertThat(buffer.toString()).isEqualTo("Hello Worldn");
}

10. @drpicox
@drpicox
@Test
public void say_hello_world() {
var buffer = new ByteArrayOutputStream();
var testOut = new PrintStream(buffer);
new HelloWorld(testOut).sayHello();
assertThat(buffer.toString()).isEqualTo("Hello Worldn");
}
HELLO WORLD
10
IMPROVE TESTING — HELLO WORLD

11. @drpicox
PATTERNS
IMPROVE TESTING 11

12. 12

13. @drpicox
@drpicox
Create one single instance, do not use static
LOWER "S" SINGLETON
13
IMPROVE TESTING — PATTERNS
// wrong
public class House {
private static House instance;
public static House getInstance() {
if (instance == null) instance = new House();
return instance;
}
}
// correct
var house = new House();

14. @drpicox
@drpicox
Ask for what you operate; do not look for things
LAW OF DEMETER
14
IMPROVE TESTING — PATTERNS
// wrong
house.getDoor().open()
// correct
door.open();

15. @drpicox
@drpicox
Give me what I need
DEPENDENCY INJECTION
15
IMPROVE TESTING — PATTERNS
// wrong (Java)
public class Clicker {
public void click() {
House.getInstance().getDoor().open();
}
}
// wrong (Javascript)
import house from './house'
export class Clicker {
click() {
house.getDoor().open();
}
}

16. @drpicox
@drpicox
Give me what I need
DEPENDENCY INJECTION
16
IMPROVE TESTING — PATTERNS
// correct
public class Clicker {
public void click(Door door) {
door.open();
}
}

17. @drpicox
@drpicox
Give me what I need
DEPENDENCY INJECTION
17
IMPROVE TESTING — PATTERNS
// better (do not breaks method signature)
public class Clicker {
private Door door;
public void Clicker(Door door) {
this.door = door;
}
public void click() {
door.open();
}
}

18. @drpicox
STATICS ARE LIARS
IMPROVE TESTING 18

19. @drpicox
@drpicox
Deceptive API
STATICS ARE LIARS
19
IMPROVE TESTING — STATICS ARE LIARS
testCharge() {
var cc = new CreditCard("123...234")
cc.charge(100);
}
Throws an exception... why?

20. @drpicox
@drpicox
Deceptive API
STATICS ARE LIARS
20
IMPROVE TESTING — STATICS ARE LIARS
testCharge() {
CreditCardProcessor.init(...);
var cc = new CreditCard("123...234")
cc.charge(100);
}
Throws an exception... why?

21. @drpicox
@drpicox
Deceptive API
STATICS ARE LIARS
21
IMPROVE TESTING — STATICS ARE LIARS
testCharge() {
OfflineQueue.start();
CreditCardProcessor.init(...);
var cc = new CreditCard("123...234")
cc.charge(100);
}
Throws an exception... why?

22. @drpicox
@drpicox
Deceptive API
STATICS ARE LIARS
22
IMPROVE TESTING — STATICS ARE LIARS
testCharge() {
Database.connect(...);
OfflineQueue.start();
CreditCardProcessor.init(...);
var cc = new CreditCard("123...234")
cc.charge(100);
}
Now works... and makes the charge...

23. @drpicox
@drpicox
Deceptive API
STATICS ARE LIARS
23
IMPROVE TESTING — STATICS ARE LIARS
testCharge() {
var db = Database();
var q = new OfflineQueue(db);
var ccp = new CreditCardProcessor(q);
var cc = new CreditCard("123...234")
cc.charge(100, ccp);
}
Now works... and makes the charge...

24. @drpicox
@drpicox
Deceptive API
STATICS ARE LIARS
24
IMPROVE TESTING — STATICS ARE LIARS
testCharge() {
var db = MockDatabase();
var q = new OfflineQueue(db);
var ccp = new CreditCardProcessor(q);
var cc = new CreditCard("123...234")
cc.charge(100, ccp);
assertThat(db).hasCharge(100, cc);
}

25. @drpicox
AVOID CODE ASSERTIONS
IMPROVE TESTING 25

26. @drpicox
@drpicox
public class House {
Door door;
Window window;
Roof roof;
Kitchen kitchen;
LivingRoom livingRoom;
BedRoom bedRoom;
House(Door door, Window window, Roof roof,
Kitchen kitchen, LivingRoom livingRoom, BedRoom bedRoom) {
this.door = Assert.notNull(door);
this.window = Assert.notNull(window);
this.roof = Assert.notNull(roof);
this.kitchen = Assert.notNull(kitchen);
this.livingRoom = Assert.notNull(livingRoom);
this.bedRoom = Assert.notNull(bedRoom);
}
void secure() {
door.lock();
window.close();
}
}
26
IMPROVE TESTING — AVOID CODE ASSERTIONS

27. @drpicox
@drpicox
public class TestHouse {
@Test
testSecureHouse() {
Door door = new Door();
Window window = new Window();
House house = new House(door, window,
new Roof(),
new Kitchen(),
new LivingRoom(),
new BedRoom());
house.secure();
assertTrue(door.isLocked());
assertTrue(window.isClosed());
}
}
27
IMPROVE TESTING — AVOID CODE ASSERTIONS
Irrelevant instances on the test
(what if they had also complex constructor?) 😱

28. @drpicox
@drpicox
public class TestHouse {
@Test
testSecureHouse() {
Door door = new Door();
Window window = new Window();
House house = new House(door, window, null, null, null, null);
house.secure();
assertTrue(door.isLocked());
assertTrue(window.isClosed());
}
}
28
IMPROVE TESTING — AVOID CODE ASSERTIONS
We do not care, faster and easier to understand

29. @drpicox
FIXING EXAMPLES
IMPROVE TESTING 29

30. @drpicox
@drpicox
public class TemperatureLogger implements Logger {
public void log(Notebook notebook) {
var weatherStation = WeatherStation.getInstance();
var thermometer = weatherStation.getThermometer();
var temperature = thermometer.getTemperature();
notebook.annotate(temperature);
}
}
// It is instantiated like this:
var logger = new TemperatureLogger();
TEMPERATURE LOGGER
30
IMPROVE TESTING — FIXING EXAMPLES

31. @drpicox
@drpicox
public class TemperatureLogger implements Logger {
private WeatherStation weatherStation;
TemperatureLogger(WeatherStation weatherStation) {
this.weatherStation = weatherStation;
}
public void log(Notebook notebook) {
var thermometer = weatherStation.getThermometer();
var temperature = thermometer.getTemperature();
notebook.annotate(temperature);
}
}
// It is instantiated like this:
var logger = new TemperatureLogger(weatherStation);
TEMPERATURE LOGGER
31
IMPROVE TESTING — FIXING EXAMPLES

32. @drpicox
@drpicox
public class TemperatureLogger implements Logger {
private Thermometer thermometer;
TemperatureLogger(Thermometer thermometer) {
this.thermometer = thermometer;
}
public void log(Notebook notebook) {
var temperature = thermometer.getTemperature();
notebook.annotate(temperature);
}
}
// It is instantiated like this:
var logger = new TemperatureLogger(
weatherStation.getThermometer()
);
TEMPERATURE LOGGER
32
IMPROVE TESTING — FIXING EXAMPLES

33. @drpicox
@drpicox
public class WheelTester {
private LegalRules legalRules;
public WheelTester(LegalRules legalRules) {
this.legalRules = legalRules;
}
public boolean checkWheels(Car car) {
Thikness thikness = legalRules.getThikness();
List<Wheel> wheels = car.getWheels();
for (Wheel wheel: wheels) {
boolean isOk = wheel.hasThikness(thikness);
if (!isOk) return false;
}
return true;
}
}
WHEEL TESTER
33
IMPROVE TESTING — FIXING EXAMPLES

34. @drpicox
@drpicox
public class WheelTester {
private Thikness thikness;
public WheelTester(Thikness thikness) {
this.thikness = thikness;
}
public boolean checkWheels(Car car) {
List<Wheel> wheels = car.getWheels();
for (Wheel wheel: wheels) {
boolean isOk = wheel.hasThikness(thikness);
if (!isOk) return false;
}
return true;
}
}
WHEEL TESTER
34
IMPROVE TESTING — FIXING EXAMPLES

35. @drpicox
@drpicox
public class WheelTester {
private Thikness thikness;
public WheelTester(Thikness thikness) {
this.thikness = thikness;
}
public boolean checkWheels(List<Wheel> wheels) {
for (Wheel wheel: wheels) {
boolean isOk = wheel.hasThikness(thikness);
if (!isOk) return false;
}
return true;
}
}
WHEEL TESTER
35
IMPROVE TESTING — FIXING EXAMPLES

36. @drpicox
@drpicox
public class HDFormatterA {
private HD hd;
public HDFormatterA() {
hd = new HardDisk();
}
public void doWork() {
hd.open();
hd.format("FAT");
hd.close();
}
}
HD FORMATTER
36
IMPROVE TESTING — FIXING EXAMPLES

37. @drpicox
@drpicox
public class HDFormatterB {
private HD hd;
public HDFormatterB() {
hd = HardDisk.getInstance();
}
public void doWork() {
hd.open();
hd.format("FAT");
hd.close();
}
}
HD FORMATTER
37
IMPROVE TESTING — FIXING EXAMPLES

38. @drpicox
@drpicox
public class HDFormatterC {
private HD hd;
public HDFormatterC() {
hd = ServiceLocator.get(HD.class);
}
public void doWork() {
hd.open();
hd.format("FAT");
hd.close();
}
}
HD FORMATTER
38
IMPROVE TESTING — FIXING EXAMPLES
public void test_hdformatterc() {
var hd = new MockHD();
ServiceLocator.set(HD.class, hd);
new HDFormatterC().doWork();
assertThat(hd.verify()).isTrue();
}

39. @drpicox
@drpicox
public class HDFormatterD {
private HD hd;
public HDFormatterD(HD hd) {
this.hd = hd;
}
public void doWork() {
hd.open();
hd.format("FAT");
hd.close();
}
}
HD FORMATTER
39
IMPROVE TESTING — FIXING EXAMPLES
public void test_hdformatterd() {
var hd = new MockHD();
new HDFormatterD().doWork(hd);
assertThat(hd.verify()).isTrue();
}

40. @drpicox
E.O.IMPROVE TESTING