ParameterizeMethod.ts

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();
        this.display.show(libraryName);
        for (const book of books) {
            this.display.show(book.getName());
        }
    }
}

//////////////////////////////////////////////
// After parameterizing the method

class Library {
    private display: Display;

    constructor(display: Display) {
        this.display = display;
    }
    
    // !! Method was parameterized and now we can test it 
    // passing a test double that overrides `readLine(): string;`
    printBooks(books: Book[], inputReader: ConsoleInputReader): void {
        const libraryName = inputReader.readLine();
        this.display.show(libraryName);
        for (const book of books) {
            this.display.show(book.getName());
        }
    }
}