Course Scenario

Estimated time to read: 5 minutes

Overview¶

This course uses a Java application implementing the business logic for the management of flights and passengers, following a set of policies.

The input for this scenario is a non-TDD working application.
The application has a suite of expected operations, however, this must be confirmed.
Unit tests will be developed around the existing code in the application.
Functionality is added by understanding what needs to be done, writing tests that initially fail, then writing code to fix the test.

Assume that you are joining the development of a program to manage flights and passengers. The company maintains supports regarding adding and removing a passenger to a flight.

Initial Application Design¶

classDiagram
 Flight --|> "has" Passenger

 class Flight {
 -String flightType
 +boolean addPassenger(Passenger passenger)
 +boolean removePassenger(Passenger passenger)
 }
 class Passenger{
 }

Business Logic¶

Passenger Addition¶

The flight may be of a few types, economy and business are known at the time, consider that there may be a need to add other types at a later time, depending on the requirements from the customer.

If the flight is an economy flight, both standard and VIP passengers may be added.

If the flight is a business flight. only VIP passengers may be added.

%%{init: {'flowchart' : {'curve' : 'linear'}}}%%

graph
 AA(( ))
 ZZ(( ))
 A[Add passenger to the flight]
 B{ }
 C{ }
 D[Approve request]
 E[Approve request]
 F[Reject request]
 G{ }
 H{ }

 AA --> A
 A --> | Is Flight Economy?| B

 B --> |Yes| D
 D --> H

 B --> | Is Passenger VIP?| C
 C --> | Yes| E
 C --> F
 E --> G
 F --> G
 G --> H

 H --> ZZ

Passenger Removal¶

There is also a policy for removing a passenger from the flight. A standard passenger may be removed from a flight, a VIP passenger cannot be removed.

%%{init: {'flowchart' : {'curve' : 'linear'}}}%%
graph
 AA(( )) --> A
 ZZ(( ))
 A[Remove passenger from flight] --> | Is passenger VIP?| B{ }
 B -->|Yes| C[Reject Request]
 B -->|No| D[Approve Request]
 E{ } --> ZZ
 C --> E
 D --> E

Conditional to Polymorphism¶

Conditional¶

classDiagram

 class Flight {
 -String flightType
 +boolean addPassenger(Passenger passenger)
 +boolean removePassenger(Passenger passenger)
 }

To test this, a switch case would have been implemented, however, as no 'default' case is given, this section of code would never be tested. Thus a polymorphic design would prove beneficial.

public boolean removePassenger(Passenger passenger) {
 switch(flightType) {
  case "Economy":
   {}
  case "Business":
   {}
  default:
   {}
 }
}

Polymorphic¶

A separate class should be introduced for each conditional type. In the example above, this shows each type of FlightType being converted into its own class.

classDiagram

 Flight <|-- EconomyFlight
 Flight <|-- BusinessFlight
 Flight <|-- PremiumFlight

 class Flight{
 +boolean addPassenger(Passenger passenger)
 +boolean removePassenger(Passenger passenger)
 }

 class EconomyFlight{

 }

 class BusinessFlight{

 }

 class PremiumFlight{

 }

Initial Codebase¶

Airport.java

package io.entityfour.tdd.airport;

public class Airport {

 public static void main(String[] args) { // Contains a main method that serves, mainly, for testing purposes
  Flight economyFlight = new Flight("1", "Economy"); // Flight 1 is Economy
  Flight businessFlight = new Flight("2", "Business"); /// Flight 2 is Business

  Passenger john = new Passenger("John", true); // VIP named John
  Passenger mike = new Passenger("Mike", false); // Standard named Mike

  businessFlight.addPassenger(john); // John is added to the flight
  businessFlight.removePassenger(john); // Then an attempt is made to remove him, this should fail due to company policy
  businessFlight.addPassenger(mike); // Mike is attempted to be added to the business flight, this should fail due to company policy
  economyFlight.addPassenger(mike); // Mike is added to the economy flight

  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());
  }
 }
}

Flight.java

package io.entityfour.tdd.airport;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Flight {

 private String id; // Flight ID
 private List<Passenger> passengersList = new ArrayList<Passenger>(); // List of passengers
 private String flightType; // Flight Type

 public Flight(String id, String flightType) {
  this.id = id;
  this.flightType = flightType;
 }

 public String getId() {
  return id;
 }

 public List<Passenger> getPassengersList() {
  return Collections.unmodifiableList(passengersList);
 }

 public String getFlightType() {
  return flightType;
 }

 public boolean addPassenger(Passenger passenger) { // Contains logic for adding a passenger
  switch (flightType) {
   case "Economy":
    return passengersList.add(passenger);
   case "Business":
    if (passenger.isVip()) {
     return passengersList.add(passenger);
    }
    return false;
   default:
    throw new RuntimeException("Unknown type: " + flightType);
  }

 }

 public boolean removePassenger(Passenger passenger) { // Contains logic for removing a passenger
  switch (flightType) {
   case "Economy":
    if (passenger.isVip()) {
     return passengersList.remove(passenger);
    }
    return false;
   case "Business":
    return false;
   default:
    throw new RuntimeException("Unknown type: " + flightType);
   }
 }

}

Passenger.java

package io.entityfour.tdd.airport;

public class Passenger {

 private String name; // Passengers Name
 private boolean vip; // VIP Flag / Status

 public Passenger(String name, boolean vip) {
  this.name = name;
  this.vip = vip;
 }

 public String getName() {
  return name;
 }

 public boolean isVip() {
  return vip;
 }

}

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
    http://maven.apache.org/maven-v4_0_0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>io.entityfour.tdd</groupId>
 <artifactId>TDD</artifactId>
 <packaging>jar</packaging>
 <version>1.0-SNAPSHOT</version>
 <name>TDD</name>
 <url>http://maven.apache.org</url>

 <build>
  <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.7.0</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <plugin>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.19.1</version>
                <dependencies>
                    <dependency>
                        <groupId>org.junit.platform</groupId>
                        <artifactId>junit-platform-surefire-provider</artifactId>
                        <version>1.0.1</version>
                    </dependency>
                </dependencies>
            </plugin>
            <plugin>
                <groupId>org.jacoco</groupId>
                <artifactId>jacoco-maven-plugin</artifactId>
                <version>0.7.9</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>prepare-agent</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>report</id>
                        <phase>test</phase>
                        <goals>
                            <goal>report</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>jacoco-check</id>
                        <phase>test</phase>
                        <goals>
                            <goal>check</goal>
                        </goals>
                        <configuration>
                            <rules>
                                <rule>
                                    <element>PACKAGE</element>
                                    <limits>
                                        <limit>
                                            <counter>LINE</counter>
                                            <value>COVEREDRATIO</value>
                                        </limit>
                                    </limits>
                                </rule>
                            </rules>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
 </build>

    <dependencies>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.0.1</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>5.0.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

</project>