Be good to yourself. Write testable code.

Transcript

1. Be good to yourself.
   Write testable code.
   

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3. SUaaS
   Suffering as a Service
   

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6. Hi, I’m Adora!
   Software Engineer, Microsoft Mixed Reality
   Writer & Youtuber, AdoraHack
   Twitter: @theadoranwodo
   

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7. Unit tests run against an individual unit of software
   @theadoranwodo
   

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8. This means we should learn to write code
   so that we can test each unit of software
   @theadoranwodo
   

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9. How do we
   write testable code?
   @theadoranwodo
   

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10. Question: How do we write testable code?
    Answer: SOLID Principles
    @theadoranwodo
    

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11. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    @theadoranwodo
    

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12. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    @theadoranwodo
    interface Input {
    Data fetch();
    }
    interface Output {
    DataObject convertToObject
    (String result);
    }
    interface ProcessManager {
    String process(Data data);
    }
    class ProcessJob {
    // ...
    ProcessJob
    (Input input, Output output, ProcessManager
    processManager
    ) {
    this.input = input;
    this.output = output;
    this.processManager = processManager;
    }
    DataOutput process() {
    Data data = this.input.get();
    String result = this.processManager
    .process(data);
    return this.output.convertToObject(result);
    }
    }
    

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13. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    @theadoranwodo
    

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14. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    @theadoranwodo
    Open to extensions and closed
    to modifications
    _______________________________
    Practice coding to abstractions,
    rather than core
    implementations
    

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15. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    Liskov Substitution Principle
    @theadoranwodo
    

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16. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    Liskov Substitution Principle
    @theadoranwodo
    Functions that use references to
    base classes must be able to use
    objects of derived classes
    without knowing it.
    

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17. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    Liskov Substitution Principle
    Interface Segregation Principle
    @theadoranwodo
    

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18. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    Liskov Substitution Principle
    Interface Segregation Principle
    @theadoranwodo
    Don’t make clients depend on
    methods they don’t use
    

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19. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    Liskov Substitution Principle
    Interface Segregation Principle
    @theadoranwodo
    interface Vehicle {
    void brake();
    void truttle();
    void clutchDown ();
    }
    class MyPrado implements Vehicle{
    void brake(){
    // code here
    }
    void clutchDown (){
    /* I don’t need this method
    but I have to implement it by force
    so I’d just throw an exception here */
    throw new UnsupportedException();
    }
    void truttle(){
    // code here
    }
    }
    Don’t do this
    

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20. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    Liskov Substitution Principle
    Interface Segregation Principle
    @theadoranwodo
    interface Vehicle {
    void brake();
    void truttle ();
    }
    interface Manual {
    void clutchDown ();
    }
    class MyPrado implements Vehicle {
    void brake(){
    // code here
    }
    void truttle (){
    // code here
    }
    }
    class MyMaserati implements Vehicle, Manual {
    void brake(){
    // code here
    }
    void clutchDown (){
    // code here
    }
    void truttle (){
    // code here
    }
    }
    Do this
    

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21. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    Liskov Substitution Principle
    Interface Segregation Principle
    Dependency Inversion Principle
    @theadoranwodo
    

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22. Question: How do we write testable code?
    Answer: SOLID Principles
    Single Responsibility Principle
    Open/Closed Principle
    Liskov Substitution Principle
    Interface Segregation Principle
    Dependency Inversion Principle
    @theadoranwodo
    High level modules should not depend
    on low level modules, both should
    depend on abstractions.
    ________________________________________
    Abstractions should not depend on
    details but details should depend on
    abstractions
    

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23. @theadoranwodo
    interface Input {
    Data fetch();
    }
    interface Output {
    DataObject convert(String result);
    }
    interface ProcessManager {
    String process(Data data);
    }
    class ProcessJob {
    // ...
    ProcessJob
    (Input input, Output output, ProcessManager
    processManager
    ) {
    this.input = input;
    this.output = output;
    this.processManager = processManager;
    }
    DataOutput process() {
    Data data = this.input.get();
    String result = this.processManager
    .process(data);
    return this.output.convert(result);
    }
    }
    ProcessJob
    Input ProcessManager
    Output
    DatabaseInput CustomProcessManager
    JSONOutput
    Interface Interface Interface
    Implementation Implementation
    Implementation
    uses uses uses
    implements implements implements
    

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24. What else can we do to make sure
    our code is testable?
    @theadoranwodo
    

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25. @theadoranwodo
    Dependency
    Injection.
    - Loosely coupled code
    - Ask for what you need, don’t look or try to create.
    - Each unit should have limited knowledge about other
    units
    

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26. @theadoranwodo
    Make sure object
    creation logic & app
    logic are different
    Your application should have two types of classes:
    - Factories for creating new objects.
    - Application classes that contain the business logic for
    your app.
    

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27. @theadoranwodo
    Respect your
    constructors
    Don’t do work in your constructors
    class Person{
    private int buildCode;
    Person(BuilderHelper helper, int seed){
    buildCode = helper.getCodeBuilder ()
    . generateCode (seed)
    . build();
    }
    }
    Don’t do this
    

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28. @theadoranwodo
    Respect your
    constructors
    Don’t do work in your constructors
    class Person{
    private int buildCode;
    Person(int buildCode){
    this.buildCode = buildCode;
    }
    }
    Do this instead
    

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29. @theadoranwodo
    Less static methods
    Avoid static methods as much as possible:
    - They are hard to test.
    - They are hard to mock.
    

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30. Code samples
    @theadoranwodo
    

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31. Let’s see a common bad real life example
    @theadoranwodo
    

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32. class Hotel
    {
    public Room getRoom(int roomId)
    {
    RoomDbClient client = RoomDbClientProvider
    .getClient();
    Room room = null;
    try {
    room = client.getRoomRecord(roomId);
    } catch(DatabaseException ex){
    ex.printStackTrace
    ();
    }
    }
    }
    class RoomDbClient implements DbClient
    {
    // more code above …
    public Room getRoomRecord(int id)
    {
    DbHelper helper = new DbHelper(“room”);
    //...
    Room room = helper.read(id);
    return room;
    //...
    }
    }
    @theadoranwodo
    

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33. class Hotel
    {
    public Room getRoom(int roomId)
    {
    RoomDbClient client = RoomDbClientProvider
    .getClient();
    Room room = null;
    try {
    room = client.getRoomRecord(roomId);
    } catch(DatabaseException ex){
    ex.printStackTrace
    ();
    }
    }
    }
    class RoomDbClient implements DbClient
    {
    // more code above …
    public Room getRoomRecord(int id)
    {
    DbHelper helper = new DbHelper(“room”);
    //...
    Room room = helper.read(id);
    return room;
    //...
    }
    }
    @theadoranwodo
    

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34. class Hotel
    {
    public Room getRoom(int roomId)
    {
    RoomDbClient client = RoomDbClientProvider
    .getClient();
    Room room = null;
    try {
    room = client.getRoomRecord(roomId);
    } catch(DatabaseException ex){
    ex.printStackTrace
    ();
    }
    }
    }
    class RoomDbClient implements DbClient
    {
    // more code above …
    public Room getRoomRecord(int id)
    {
    DbHelper helper = new DbHelper(“room”);
    //...
    Room room = helper.read(id);
    return room;
    //...
    }
    }
    @theadoranwodo
    

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35. class Hotel
    {
    public Room getRoom(int roomId)
    {
    RoomDbClient client = RoomDbClientProvider
    .getClient();
    Room room = null;
    try {
    room = client.getRoomRecord(roomId);
    } catch(DatabaseException ex){
    ex.printStackTrace
    ();
    }
    }
    }
    class RoomDbClient implements DbClient
    {
    // more code above …
    public Room getRoomRecord(int id)
    {
    DbHelper helper = new DbHelper(“room”);
    //...
    Room room = helper.read(id);
    return room;
    //...
    }
    }
    @theadoranwodo
    

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36. Now, let’s see a basic foobar example
    @theadoranwodo
    

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37. class Foo
    {
    public Bar getBar(int barId)
    {
    Rabbit rabbit = new Rabbit();
    Animal animal = new Animal();
    Bar bar = animal.doSomething (barId, rabbit);
    return bar;
    }
    }
    @theadoranwodo
    

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38. class Foo
    {
    public Bar getBar(int barId)
    {
    Rabbit rabbit = new Rabbit();
    Animal animal = new Animal();
    Bar bar = animal.doSomething (barId, rabbit);
    return bar;
    }
    }
    @theadoranwodo
    

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39. class Foo
    {
    private final Rabbit rabbit;
    private final Animal animal;
    public Foo(RabbitFactory rabbitFactory, AnimalFactory animalFactory ){
    this.rabbit = rabbitFactory .Create();
    this.animal = animalFactory .Create();
    }
    // more code …
    public Bar getBar(int barId)
    {
    Bar bar = animal.doSomething (barId, rabbit );
    return bar;
    }
    }
    @theadoranwodo
    

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40. This is Jennifer.
    Jennifer writes testable code.
    Her team members love her because it’s easy to understand and test her code.
    Jennifer is a great Engineer.
    Be like Jennifer.
    @theadoranwodo
    

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41. Thank you!
    www.adoranwodo.com
    @theadoranwodo
    

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