应该在简单实体中测试什么（TDD）？

I am learning code testing (TDD) and wondering what should be tested for simple entities in Symfony?

From official documentation:

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * Category
 *
 * @ORM\Table(name="category")
 * @ORM\Entity(repositoryClass="AppBundle\Repository\CategoryRepository")
 */
class Category
{
    /**
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\Column(name="name", type="string", length=255)
     */
    private $name;

    /**
     * @ORM\OneToMany(targetEntity="Product", mappedBy="category")
     */
    private $products;
    /**
     * Constructor
     */
    public function __construct()
    {
        $this->products = new \Doctrine\Common\Collections\ArrayCollection();
    }

    /**
     * Get id
     *
     * @return integer
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Set name
     *
     * @param string $name
     *
     * @return Category
     */
    public function setName($name)
    {
        $this->name = $name;

        return $this;
    }

    /**
     * Get name
     *
     * @return string
     */
    public function getName()
    {
        return $this->name;
    }

    /**
     * Add product
     *
     * @param \AppBundle\Entity\Product $product
     *
     * @return Category
     */
    public function addProduct(\AppBundle\Entity\Product $product)
    {
        $this->products[] = $product;

        return $this;
    }

    /**
     * Remove product
     *
     * @param \AppBundle\Entity\Product $product
     */
    public function removeProduct(\AppBundle\Entity\Product $product)
    {
        $this->products->removeElement($product);
    }

    /**
     * Get products
     *
     * @return \Doctrine\Common\Collections\Collection
     */
    public function getProducts()
    {
        return $this->products;
    }
}

Second:

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="product")
 */
class Product
{
    /**
     * @ORM\Column(type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\Column(type="string", length=100)
     */
    private $name;

    /**
     * @ORM\Column(type="decimal", scale=2)
     */
    private $price;

    /**
     * @ORM\Column(type="text")
     */
    private $description;

    /**
     * @ORM\ManyToOne(targetEntity="Category", inversedBy="products")
     * @ORM\JoinColumn(name="category_id", referencedColumnName="id")
     */
    private $category;

    /**
     * Get id
     *
     * @return integer
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Set name
     *
     * @param string $name
     *
     * @return Product
     */
    public function setName($name)
    {
        $this->name = $name;

        return $this;
    }

    /**
     * Get name
     *
     * @return string
     */
    public function getName()
    {
        return $this->name;
    }

    /**
     * Set price
     *
     * @param string $price
     *
     * @return Product
     */
    public function setPrice($price)
    {
        $this->price = $price;

        return $this;
    }

    /**
     * Get price
     *
     * @return string
     */
    public function getPrice()
    {
        return $this->price;
    }

    /**
     * Set description
     *
     * @param string $description
     *
     * @return Product
     */
    public function setDescription($description)
    {
        $this->description = $description;

        return $this;
    }

    /**
     * Get description
     *
     * @return string
     */
    public function getDescription()
    {
        return $this->description;
    }

    /**
     * Set category
     *
     * @param \AppBundle\Entity\Category $category
     *
     * @return Product
     */
    public function setCategory(\AppBundle\Entity\Category $category = null)
    {
        $this->category = $category;

        return $this;
    }

    /**
     * Get category
     *
     * @return \AppBundle\Entity\Category
     */
    public function getCategory()
    {
        return $this->category;
    }
}

I thought I had to create an Entity folder and within CategoryTest file:

namespace Tests\AppBundle\Entity;

use AppBundle\Entity\Tag;
use AppBundle\Form\DataTransformer\TagArrayToStringTransformer;
use Doctrine\Common\Persistence\ObjectManager;
use Doctrine\ORM\EntityRepository;

class CategoryTest extends \PHPUnit\Framework\TestCase
{
    public function testGetName()
    {
        $category = new \AppBundle\Entity\Category();
        $category->setName('test');
        $this->assertSame('test', $category->getName());
    }
}

So... In TDD I should testing all fields? For Product entity I should testing name, price and description?

If yes, how to deal with refactoring? In these cases I must use in all methods "$product = new Product();";

For a name field I might need to do another test? What?

Should I also test relationships or do it in functional tests?

It is a good practice to Entities have no (complex) logic inside. In fact it should be just representing your model. And since there is no logic, there is not much to test actually. When you check Symfony Demo app you will find no tests for entities and I believe it is done this way intentionally.

In case your application is not the only one using database I would consider writing functional tests for entities which will ensure you that someone else did not change database structure (for example by dropping column in table) without letting you know. One of possible ways to achieve that is running a simple query on table (entity) you are testing:

public function checkEntityDefinition($entityName)
{         $this->em->getRepository($entityName)
            ->createQueryBuilder('t')
            ->setMaxResults(1)
            ->getQuery()
            ->getArrayResult();
}

There are no assertion here but this will throw an exception when Entity definition does not match database