trikitrok

class Library {
    private readonly display: Display;

    constructor(display: Display) {
        this.display = display;
    }

    // we don't want to use a test double of an interface we don't own
    printBooks(books: Book[], inputReader: AcmeInputReader): void {
        const libraryName = inputReader.readLine();

trikitrok

class Library {
    private display: Display;

    constructor(display: Display) {
        this.display = display;
    }

    printBooks(books: Book[]): void {
        const inputReader = new ConsoleInputReader(); // creating the ConsoleInputReader here impedes unit testing
        const libraryName = inputReader.readLine();

trikitrok

// We'd like to test PaydayTransaction which 
// depends on a concrete class: TransactionLog

class TransactionLog {
    public saveTransaction(paydayTransaction: PaydayTransaction): void {
        // persist the transaction
        // ...
    }
}

trikitrok

Wrap class.

How to do it:

1. Identify the change point.

2. Create a class that accepts the class we are going to wrap as a constructor argument.

   • If we have trouble creating the original class in a test harness, we might have to use Extract Interface on the wrapped class so that we can instantiate the wrapper.

3. Create a method on the wrapper class with tests, that implements the new behaviour.

trikitrok

Sprout class.

How to do it:

1. Identify the change point and determine the sprouted class interface.

   • Pass to the sprouted class’s constructor any source method’s local variables it needs as parameters.

   • Determine whether the sprouted class’ method will need to return values to the source method.

trikitrok

Wrap method.

Version 1 (when clients will only use the composed behaviour).

How to do it:

1. Identify the change point.

2. Extract a method with the body of the current method.

trikitrok

Sprout method.

How to do it:

1. Identify the change point and determine the sprouted method signature (input/output).

   • Pass to the sprouted method any source method’s local variables it needs as parameters.

   • Determine whether the sprouted method will need to return values to any variable in the source method.

trikitrok

<?php

interface Customer {
    public function getEarnedDiscount(): float;

    public function addToOrdersHistory(Order $order): void;
}

// Null Customer's implementation
class NotFoundCustomer implements Customer {

trikitrok

public interface Customer
{
    double GetEarnedDiscount();

    void AddToOrdersHistory(Order order);
}

// Null Customer's implementation
public class NotFoundCustomer : Customer
{

trikitrok

public interface Customer {
    double getEarnedDiscount();

    void addToOrdersHistory(Order order);
}

// Null Customer's implementation
public class NotFoundCustomer implements Customer {
    private final double DEFAULT_DISCOUNT = 1.0;