TDD의 핵심 개념
TDD란 요구 사항을 테스트로 뽑아 낸 다음, 테스트를 통과하는 프로그램을 개발하는 과정을 되도록 짧게 반복하는 프로그래밍 기법이다.
TDD는 작동하는 클린 코드를 추구함으로써 단순한 설계를 유도하고 소프트웨어의 안정성을 제고한다.
따라서 TDD는 다음과 같은 개발 주기를 가진다.
✏️ 테스트한다, 코드를 작성한다, 리팩터링한다, (반복한다) ...
리팩터링은 소스 코드의 외부 동작에는 영향을 주지 않고 내부 구조만을 개선하는 방식으로 소프트웨어를 수정하는 작업이다. 이때 외부 동작에 영향을 주지 않는다는 것을 증명하기 위해서 테스트를 사용할 수 있다.
- 장점
- 분명한 목표를 가지고 코드를 짤 수 있을뿐더러, 애플리케이션이 해야 하는 일만 정확하게 개발할 수 있다.
- 기존의 소스 코드에 버그가 생기는 것은 막아 주면서, 새로운 기능을 빠르게 개발할 수 있다. 테스트는 해야 할 일만 정확하게 하는 코드를 구현하도록 유도하는 힘이 있다.
- 테스트는 애플리케이션의 설계 명세로 기능한다. 개발자는 테스트를 통해 해결해야 하는 과제가 무엇인지 이해할 수 있다.
TDD를 통한 리팩터링 예제 - 기존 소스를 개선
📕 요구사항
✔️ 현재 항공편은 이코노미와 비즈니스로 구분된다. 항공편에 언제든지 다른 종류의 항공편이 추가될 가능성이 있다.
✔️ 이코노미 항공편은 VIP 승객과 일반 승객 모두 이용가능하지만, 비즈니스 항공편은 VIP 승객만 이용 가능하다.
✔️ 항공편에서 일반 승객은 삭제할 수 있지만 VIP 승객은 삭제할 수 없다.
📕 AS-IS 현황
- Passenger
public class Passenger {
private String name;
private boolean vip;
public Passenger(String name, boolean vip) {
this.name = name;
this.vip = vip;
}
public String getName() {
return name;
}
public boolean isVip() {
return vip;
}
}
- Flight
package com.manning.junitbook.airport;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Flight {
private String id;
private List<Passenger> passengers = new ArrayList<Passenger>();
private String flightType;
public Flight(String id, String flightType) {
this.id = id;
this.flightType = flightType;
}
public String getId() {
return id;
}
public List<Passenger> getPassengersList() {
return Collections.unmodifiableList(passengers);
}
public String getFlightType() {
return flightType;
}
// 주어진 조건에 따라 Passenger를 추가
public boolean addPassenger(Passenger passenger) {
switch (flightType) {
case "Economy":
return passengers.add(passenger);
case "Business":
if (passenger.isVip()) {
return passengers.add(passenger);
}
return false;
default:
throw new RuntimeException("Unknown type: " + flightType);
}
}
public boolean removePassenger(Passenger passenger) {
switch (flightType) {
case "Economy":
if (!passenger.isVip()) {
return passengers.remove(passenger);
}
return false;
case "Business":
return false;
default:
throw new RuntimeException("Unknown type: " + flightType);
}
}
}
- 테스트 코드의 역할을 하는 Airport 클래스
public class Airport {
public static void main(String[] args) {
Flight economyFlight = new Flight("1", "Economy");
Flight businessFlight = new Flight("2", "Business");
Passenger james = new Passenger("James", true);
Passenger mike = new Passenger("Mike", false);
businessFlight.addPassenger(james);
businessFlight.removePassenger(james);
businessFlight.addPassenger(mike);
economyFlight.addPassenger(mike);
System.out.println("Business flight passengers list:");
for (Passenger passenger : businessFlight.getPassengersList()) {
System.out.println(passenger.getName());
}
System.out.println("Economy flight passengers list:");
for (Passenger passenger : economyFlight.getPassengersList()) {
System.out.println(passenger.getName());
}
}
}
📕 TO-BE 🔨 TDD 를 추가
- TDD 추가
public class AirportTest {
@DisplayName("Given there is an economy flight")
@Nested
class EconomyFlightTest {
private Flight economyFlight;
@BeforeEach
void setUp() {
economyFlight = new Flight("1", "Economy");
}
@Test
public void testEconomyFlightRegularPassenger() {
Passenger mike = new Passenger("Mike", false);
assertEquals("1", economyFlight.getId());
assertEquals(true, economyFlight.addPassenger(mike));
assertEquals(1, economyFlight.getPassengersList().size());
assertEquals("Mike", economyFlight.getPassengersList().get(0).getName());
assertEquals(true, economyFlight.removePassenger(mike));
assertEquals(0, economyFlight.getPassengersList().size());
}
@Test
public void testEconomyFlightVipPassenger() {
Passenger james = new Passenger("James", true);
assertEquals("1", economyFlight.getId());
assertEquals(true, economyFlight.addPassenger(james));
assertEquals(1, economyFlight.getPassengersList().size());
assertEquals("James", economyFlight.getPassengersList().get(0).getName());
assertEquals(false, economyFlight.removePassenger(james));
assertEquals(1, economyFlight.getPassengersList().size());
}
}
@DisplayName("Given there is a business flight")
@Nested
class BusinessFlightTest {
private Flight businessFlight;
@BeforeEach
void setUp() {
businessFlight = new Flight("2", "Business");
}
@Test
public void testBusinessFlightRegularPassenger() {
Passenger mike = new Passenger("Mike", false);
assertEquals(false, businessFlight.addPassenger(mike));
assertEquals(0, businessFlight.getPassengersList().size());
assertEquals(false, businessFlight.removePassenger(mike));
assertEquals(0, businessFlight.getPassengersList().size());
}
@Test
public void testBusinessFlightVipPassenger() {
Passenger james = new Passenger("James", true);
assertEquals(true, businessFlight.addPassenger(james));
assertEquals(1, businessFlight.getPassengersList().size());
assertEquals(false, businessFlight.removePassenger(james));
assertEquals(1, businessFlight.getPassengersList().size());
}
}
}
해당 코드들의 테스트 커버리지를 측정해보면, 기존에 있었던 Airport 클래스의 테스트 커버리지는 0%에 해당한다. 또한 Flight 클래스의 커버리지도 100%를 만족하지 못한다.
또한 항공편이 이코노미도, 비즈니스도 아닌 경우 ( Flight의 switch 문에서 default 에 해당 ) 커버되지 않는 모습을 볼 수 있다. 이렇듯 테스트 코드를 통해 커버리지를 측정하면, 리팩터링이 필요한 부분을 확인할 수 있다.
📕 TO-BE 🔨 리팩터링 수행하기
테스트 커버리지 측정에서, Flight 클래스의 flightType 필드의 리팩터링 필요성을 알 수 있었다. AS-IS 에서는 switch 문을 통해 flightType 별로 탑승객 추가 여부를 판단하였으나, 리팩터링한 코드에서는 switch 분기문 대신 다형성을 적용할 것이다.
변경할 항목은 다음과 같다.
✔️ Flight 의 addPassenger 와 removePassenger을 추상 메서드로 변경하여 구체적인 구현을 하위 클래스에서 하도록 변경
✔️ flightType 필드를 삭제하고, flghtType에 대응되도록 Flight의 하위 클래스를 별도로 생성
- Flight
public abstract class Flight {
private String id;
Set<Passenger> passengers = new HashSet<>();
public Flight(String id) {
this.id = id;
}
public String getId() {
return id;
}
public Set<Passenger> getPassengersSet() {
return Collections.unmodifiableSet(passengers);
}
public abstract boolean addPassenger(Passenger passenger);
public abstract boolean removePassenger(Passenger passenger);
}
- Flight 를 구현한 EconomyFlight
public class EconomyFlight extends Flight {
public EconomyFlight(String id) {
super(id);
}
@Override
public boolean addPassenger(Passenger passenger) {
return passengers.add(passenger);
}
@Override
public boolean removePassenger(Passenger passenger) {
if (!passenger.isVip()) {
return passengers.remove(passenger);
}
return false;
}
}
- Flight 를 구현한 BusinessFlight
public class BusinessFlight extends Flight {
public BusinessFlight(String id) {
super(id);
}
@Override
public boolean addPassenger(Passenger passenger) {
if (passenger.isVip()) {
return passengers.add(passenger);
}
return false;
}
@Override
public boolean removePassenger(Passenger passenger) {
return false;
}
}
- 변경된 테스트 코드
public class AirportTest {
@DisplayName("Given there is an economy flight")
@Nested
class EconomyFlightTest {
private Flight economyFlight;
@BeforeEach
void setUp() {
economyFlight = new EconomyFlight("1");
}
@Test
public void testEconomyFlightRegularPassenger() {
Passenger mike = new Passenger("Mike", false);
assertEquals("1", economyFlight.getId());
assertEquals(true, economyFlight.addPassenger(mike));
assertEquals(1, economyFlight.getPassengers().size());
assertEquals("Mike", economyFlight.getPassengers().get(0).getName());
assertEquals(true, economyFlight.removePassenger(mike));
assertEquals(0, economyFlight.getPassengers().size());
}
@Test
public void testEconomyFlightVipPassenger() {
Passenger james = new Passenger("James", true);
assertEquals("1", economyFlight.getId());
assertEquals(true, economyFlight.addPassenger(james));
assertEquals(1, economyFlight.getPassengers().size());
assertEquals("James", economyFlight.getPassengers().get(0).getName());
assertEquals(false, economyFlight.removePassenger(james));
assertEquals(1, economyFlight.getPassengers().size());
}
}
@DisplayName("Given there is a business flight")
@Nested
class BusinessFlightTest {
private Flight businessFlight;
@BeforeEach
void setUp() {
businessFlight = new BusinessFlight("2");
}
@Test
public void testBusinessFlightRegularPassenger() {
Passenger mike = new Passenger("Mike", false);
assertEquals(false, businessFlight.addPassenger(mike));
assertEquals(0, businessFlight.getPassengers().size());
assertEquals(false, businessFlight.removePassenger(mike));
assertEquals(0, businessFlight.getPassengers().size());
}
@Test
public void testBusinessFlightVipPassenger() {
Passenger james = new Passenger("James", true);
assertEquals(true, businessFlight.addPassenger(james));
assertEquals(1, businessFlight.getPassengers().size());
assertEquals(false, businessFlight.removePassenger(james));
assertEquals(1, businessFlight.getPassengers().size());
}
}
}
TDD를 통한 리팩터링 예제 - 신규 기능 추가 및 보완
📕 요구사항
✔️ 프리미엄 항공편을 추가한다.
✔️ 프리미엄 항공편에는 VIP 승객만 추가할 수 있다.
✔️ 프리미엄 항공편에서는 승객 삭제가 가능하다
✔️ 항공편에 승객은 중복으로 등록될 수 없다.
- PremiumFlight 추가
package com.manning.junitbook.airport;
public class PremiumFlight extends Flight {
public PremiumFlight(String id) {
super(id);
}
@Override
public boolean addPassenger(Passenger passenger) {
if (passenger.isVip()) {
return passengers.add(passenger);
}
return false;
}
@Override
public boolean removePassenger(Passenger passenger) {
if (passenger.isVip()) {
return passengers.remove(passenger);
}
return false;
}
}
- 개선된 테스트 코드
public class AirportTest {
@DisplayName("Given there is an economy flight")
@Nested
class EconomyFlightTest {
private Flight economyFlight;
private Passenger mike;
private Passenger james;
@BeforeEach
void setUp() {
economyFlight = new EconomyFlight("1");
mike = new Passenger("Mike", false);
james = new Passenger("James", true);
}
@Nested
@DisplayName("When we have a regular passenger")
class RegularPassenger {
@Test
@DisplayName("Then you can add and remove him from an economy flight")
public void testEconomyFlightRegularPassenger() {
assertAll("Verify all conditions for a regular passenger and an economy flight",
() -> assertEquals("1", economyFlight.getId()),
() -> assertEquals(true, economyFlight.addPassenger(mike)),
() -> assertEquals(1, economyFlight.getPassengersSet().size()),
() -> assertEquals("Mike", new ArrayList<>(economyFlight.getPassengersSet()).get(0).getName()),
() -> assertEquals(true, economyFlight.removePassenger(mike)),
() -> assertEquals(0, economyFlight.getPassengersSet().size())
);
}
@DisplayName("Then you cannot add him to an economy flight more than once")
@RepeatedTest(5)
public void testEconomyFlightRegularPassengerAddedOnlyOnce(RepetitionInfo repetitionInfo) {
for (int i = 0; i < repetitionInfo.getCurrentRepetition(); i++) {
economyFlight.addPassenger(mike);
}
assertAll("Verify a regular passenger can be added to an economy flight only once",
() -> assertEquals(1, economyFlight.getPassengersSet().size()),
() -> assertTrue(economyFlight.getPassengersSet().contains(mike)),
() -> assertTrue(new ArrayList<>(economyFlight.getPassengersSet()).get(0).getName().equals("Mike"))
);
}
}
@Nested
@DisplayName("When we have a VIP passenger")
class VipPassenger {
@Test
@DisplayName("Then you can add him but cannot remove him from an economy flight")
public void testEconomyFlightVipPassenger() {
assertAll("Verify all conditions for a VIP passenger and an economy flight",
() -> assertEquals("1", economyFlight.getId()),
() -> assertEquals(true, economyFlight.addPassenger(james)),
() -> assertEquals(1, economyFlight.getPassengersSet().size()),
() -> assertEquals("James", new ArrayList<>(economyFlight.getPassengersSet()).get(0).getName()),
() -> assertEquals(false, economyFlight.removePassenger(james)),
() -> assertEquals(1, economyFlight.getPassengersSet().size())
);
}
@DisplayName("Then you cannot add him to an economy flight more than once")
@RepeatedTest(5)
public void testEconomyFlightVipPassengerAddedOnlyOnce(RepetitionInfo repetitionInfo) {
for (int i = 0; i < repetitionInfo.getCurrentRepetition(); i++) {
economyFlight.addPassenger(james);
}
assertAll("Verify a VIP passenger can be added to an economy flight only once",
() -> assertEquals(1, economyFlight.getPassengersSet().size()),
() -> assertTrue(economyFlight.getPassengersSet().contains(james)),
() -> assertTrue(new ArrayList<>(economyFlight.getPassengersSet()).get(0).getName().equals("James"))
);
}
}
}
@DisplayName("Given there is a business flight")
@Nested
class BusinessFlightTest {
private Flight businessFlight;
private Passenger mike;
private Passenger james;
@BeforeEach
void setUp() {
businessFlight = new BusinessFlight("2");
mike = new Passenger("Mike", false);
james = new Passenger("James", true);
}
@Nested
@DisplayName("When we have a regular passenger")
class RegularPassenger {
@Test
@DisplayName("Then you cannot add or remove him from a business flight")
public void testBusinessFlightRegularPassenger() {
assertAll("Verify all conditions for a regular passenger and a business flight",
() -> assertEquals(false, businessFlight.addPassenger(mike)),
() -> assertEquals(0, businessFlight.getPassengersSet().size()),
() -> assertEquals(false, businessFlight.removePassenger(mike)),
() -> assertEquals(0, businessFlight.getPassengersSet().size())
);
}
}
@Nested
@DisplayName("When we have a VIP passenger")
class VipPassenger {
@Test
@DisplayName("Then you can add him but cannot remove him from a business flight")
public void testBusinessFlightVipPassenger() {
assertAll("Verify all conditions for a VIP passenger and a business flight",
() -> assertEquals(true, businessFlight.addPassenger(james)),
() -> assertEquals(1, businessFlight.getPassengersSet().size()),
() -> assertEquals(false, businessFlight.removePassenger(james)),
() -> assertEquals(1, businessFlight.getPassengersSet().size())
);
}
@DisplayName("Then you cannot add him to a business flight more than once")
@RepeatedTest(5)
public void testBusinessFlightVipPassengerAddedOnlyOnce(RepetitionInfo repetitionInfo) {
for (int i = 0; i < repetitionInfo.getCurrentRepetition(); i++) {
businessFlight.addPassenger(james);
}
assertAll("Verify a VIP passenger can be added to a business flight only once",
() -> assertEquals(1, businessFlight.getPassengersSet().size()),
() -> assertTrue(businessFlight.getPassengersSet().contains(james)),
() -> assertTrue(new ArrayList<>(businessFlight.getPassengersSet()).get(0).getName().equals("James"))
);
}
}
}
@DisplayName("Given there is a premium flight")
@Nested
class PremiumFlightTest {
private Flight premiumFlight;
private Passenger mike;
private Passenger james;
@BeforeEach
void setUp() {
premiumFlight = new PremiumFlight("3");
mike = new Passenger("Mike", false);
james = new Passenger("James", true);
}
@Nested
@DisplayName("When we have a regular passenger")
class RegularPassenger {
@Test
@DisplayName("Then you cannot add or remove him from a premium flight")
public void testPremiumFlightRegularPassenger() {
assertAll("Verify all conditions for a regular passenger and a premium flight",
() -> assertEquals(false, premiumFlight.addPassenger(mike)),
() -> assertEquals(0, premiumFlight.getPassengersSet().size()),
() -> assertEquals(false, premiumFlight.removePassenger(mike)),
() -> assertEquals(0, premiumFlight.getPassengersSet().size())
);
}
}
@Nested
@DisplayName("When we have a VIP passenger")
class VipPassenger {
@Test
@DisplayName("Then you can add and remove him from a premium flight")
public void testPremiumFlightVipPassenger() {
assertAll("Verify all conditions for a VIP passenger and a premium flight",
() -> assertEquals(true, premiumFlight.addPassenger(james)),
() -> assertEquals(1, premiumFlight.getPassengersSet().size()),
() -> assertEquals(true, premiumFlight.removePassenger(james)),
() -> assertEquals(0, premiumFlight.getPassengersSet().size())
);
}
@DisplayName("Then you cannot add him to a premium flight more than once")
@RepeatedTest(5)
public void testPremiumFlightVipPassengerAddedOnlyOnce(RepetitionInfo repetitionInfo) {
for (int i = 0; i < repetitionInfo.getCurrentRepetition(); i++) {
premiumFlight.addPassenger(james);
}
assertAll("Verify a VIP passenger can be added to a premium flight only once",
() -> assertEquals(1, premiumFlight.getPassengersSet().size()),
() -> assertTrue(premiumFlight.getPassengersSet().contains(james)),
() -> assertTrue(new ArrayList<>(premiumFlight.getPassengersSet()).get(0).getName().equals("James"))
);
}
}
}
}