BookRepositoryTest.php

<?php

class BookRepository
{
    protected $book;

    public function __construct(Book $book)
    {
        $this->book = $book;
    }

    public function getFlaggedBooks()
    {
        return $this->book->flagged()->get();
    }
}

class BookRepositoryTest extends \TestCase
{
    public function setUp()
    {
        parent::setUp();
        $this->repository = app(BookRepository::class);
    }

    /** @test */
    public function it_gets_flagged_books()
    {
        // cria dois livros, um flagged e outro não
        $book = factory(App\Book::class)->create();
        $flaggedBook = factory(App\Book::class)->create(['flagged' => 1]);

        $books = $this->repository->getFlaggedBooks();

        // confirma que apenas o livro flagged foi retornado
        $this->assertEquals(1, $books->count());
        $this->assertEquals($flaggedBook->fresh(), $books->first());
    }
}