How to unit test Eloquent relationships

In my opinion, Eloquent is one of the most powerful features of Laravel. It is an API for interacting with your database, and it has a very nice and easy-to-remember syntax. For example:

$post->author->name;

Will give you the name of the post's author.

This is an example of an Eloquent relationship. Relationships define how your models (tables) are connected. Although most are easy to understand, there are a few more complicated ones.

If you want to learn more about relationships themself, click here and click here for polymorphic relationships.

One to one (has one)

In this example, we have two models: a User and an Address.

• A User has one Address
• An Address belongs to a User

You can test this relationship from the User model like this:

// tests/Unit/Models/UserTest.php

use App\Models\Address;
use App\Models\User;

/** @test */
public function a_user_has_one_address()
{
    $user = User::factory()->create();
    $address = Address::factory()->create(['user_id' => $user->id]);

    $this->assertInstanceOf(Address::class, $user->address);
    $this->assertEquals($address->id, $user->address_id);
}

One to one inverse (belongs to)

In this example, we have two models: a User and an Address.

• A User has one Address
• An Address belongs to a User

You can test this relationship from the Address model like this:

// tests/Unit/Models/AddressTest.php

use App\Models\Address;
use App\Models\User;

/** @test */
public function an_address_belongs_to_a_user()
{
    $user = User::factory()->create();
    $address = Address::factory()->create(['user_id' => $user->id]);

    $this->assertEquals($user->id, $address->user_id);
    $this->assertInstanceOf(User::class, $address->user);
    $this->assertEquals($user->id, $address->user->id);
}

One to many (has many)

In this example, we have two models: a Post and a Category.

• A Post belongs to a Category
• A Category has many Posts

You can test this relationship from the Category model like this:

// tests/Unit/Models/CategoryTest.php

use App\Models\Category;
use App\Models\Post;
use Illuminate\Database\Eloquent\Collection;

/** @test */
public function a_category_has_many_posts()
{
    $category = Category::factory()->create();
    $post = Post::factory()->create(['category_id' => $category->id]);

    $this->assertInstanceOf(Collection::class, $category->posts);
    $this->assertInstanceOf(Post::class, $category->posts->first);
    $this->assertEquals($post->id, $category->posts->first()->id);
}

Has many through

In this example, we have three models: an Author, a Post, and a Language.

• A Post belongs to an Author
• An Author has many Posts
• An Author "belongs" to a Language (speaks a language)
• A Language has many Authors

You can test this relationship from the Language model like this:

// tests/Unit/Models/LanguageTest.php

use App\Models\Language;
use App\Models\User;
use App\Models\Post;
use Illuminate\Database\Eloquent\Collection;

/** @test */
public function a_language_has_many_posts()
{
    $language = Language::factory()->create();
    $user = User::factory()->create(['language_id' => $language->id]);
    $post = Post::factory()->create(['user_id' => $user->id]);

    $this->assertInstanceOf(Collection::class, $language->posts);
    $this->assertInstanceOf(Post::class, $language->posts->first);
    $this->assertEquals($post->id, $language->posts->first()->id);
}

Many to many (belongs to many)

In this example, we have two models: a Product and a Tag.

• A Product has many Tags
• A Tag has many Products

You can test this relationship from the Product model like this:

// tests/Unit/Models/ProductTest.php

use App\Models\Product;
use App\Models\Tag;
use Illuminate\Database\Eloquent\Collection;

/** @test */
public function a_product_has_many_tags()
{
    $product = Product::factory()->create();
    $tag = Tag::factory()->create();
    $product->tags->attach($tag);

    $this->assertInstanceOf(Collection::class, $product->tags);
    $this->assertInstanceOf(Tag::class, $product->tags->first);
    $this->assertEquals($tag->id, $product->tags->first()->id);
}

Polymorphic: one to one

In this example, we have three models: a Post, a Video, and an Image.

• A Post has one Image
• A Video has one Image
• An Image belongs to a Post or a Video

You can test this relationship from the Post (or the Video) model like this:

// tests/Unit/Models/PostTest.php

use App\Models\Post;
use App\Models\Image;

/** @test */
public function a_post_has_one_image()
{
    $post = Post::factory()->create();
    $image = Image::factory()->create([
        'imageable_type' => 'App\Models\Post',
        'imageable_id' => $post->id
    ]);

    $this->assertInstanceOf(Image::class, $post->image);
    $this->assertEquals($image->id, $post->image->id);
}

And you can test this relationship from the Image model like this:

// tests/Unit/Models/ImageTest.php

use App\Models\Image;
use App\Models\Post;
use App\Models\Video;

/** @test */
public function an_image_belongs_to_a_post_or_a_video()
{
    $post = Post::factory()->create();
    $image = Image::factory()->create([
        'imageable_type' => 'App\Models\Post',
        'imageable_id' => $post->id
    ]);

    $this->assertInstanceOf(Post::class, $image->imageable);
    $this->assertEquals($post->id, $image->imageable);

    $video = Video::factory()->create();
    $image = Image::factory()->create([
        'imageable_type' => 'App\Models\Video',
        'imageable_id' => $video->id
    ]);

    $this->assertInstanceOf(Video::class, $image->imageable);
    $this->assertEquals($video->id, $image->imageable);
}

Polymorphic: one to many

In this example, we have three models: a Post, a Video, and a Comment.

• A Post has many Comments
• A Video has many Comments
• A Comment belongs to a Post or a Video

You can test this relationship from the Post (or the Video) model like this:

// tests/Unit/Models/PostTest.php

use App\Models\Comment;
use App\Models\Post;
use Illuminate\Database\Eloquent\Collection;

/** @test */
public function a_post_has_many_comments()
{
    $post = Post::factory()->create();
    $comment = Comment::factory()->create([
        'commentable_type' => 'App\Models\Post',
        'commentable_id' => $post->id
    ]);

    $this->assertInstanceOf(Collection::class, $post->comments);
    $this->assertInstanceOf(Comment::class, $post->comments->first());
    $this->assertEquals($comment->id, $post->comments->first()->id);
}

And you can test this relationship from the Comment model like this:

// tests/Unit/Models/CommentTest.php

use App\Models\Comment;
use App\Models\Post;
use App\Models\Video;
use Illuminate\Database\Eloquent\Collection;

/** @test */
public function a_comment_belongs_to_a_post_or_video()
{
    $post = Post::factory()->create();
    $comment = Comment::factory()->create([
        'commentable_type' => 'App\Models\Post',
        'commentable_id' => $post->id
    ]);

    $this->assertInstanceOf(Post::class, $comment->post);
    $this->assertEquals($post->id, $comment->commentable->id);

    $video = Video::factory()->create();
    $comment = Comment::factory()->create([
        'commentable_type' => 'App\Models\Video',
        'commentable_id' => $video->id
    ]);

    $this->assertInstanceOf(Video::class, $comment->video);
    $this->assertEquals($video->id, $comment->commentable->id);
}

Polymorphic: many to many

In this example, we have three models: a Post, a Video, and a Tag.

• A Post has many Tags
• A Video has many Tags
• A Tag belongs to many Posts or Videos

You can test this relationship from the Post (or the Video) model like this:

// tests/Unit/Models/CommentTest.php

use App\Models\Tag;
use App\Models\Post;
use Illuminate\Database\Eloquent\Collection;

/** @test */
public function a_post_has_many_tags()
{
    $post = Post::factory()->create();
    $tag = Tag::factory()->create();
    $post->tags->attach($tag);

    $this->assertInstanceOf(Collection::class, $post->tags);
    $this->assertInstanceOf(Tag::class, $post->tags->first());
    $this->assertEquals($tag->id, $post->tags->first()->id);
}

And you can test this relationship from the Tag model like this:

// tests/Unit/Models/CommentTest.php

use App\Models\Tag;
use App\Models\Post;
use Illuminate\Database\Eloquent\Collection;

/** @test */
public function a_tag_has_many_posts_and_videos()
{
    $tag = Tag::factory()->create();

    $post = Post::factory()->create();
    $post->tags->attach($tag);

    $this->assertInstanceOf(Collection::class, $tag->posts);
    $this->assertInstanceOf(Post::class, $tag->posts->first());
    $this->assertEquals($post->id, $tag->posts->first()->id);

    $video = Video::factory()->create();
    $video->tags->attach($tag);

    $this->assertInstanceOf(Collection::class, $tag->videos);
    $this->assertInstanceOf(Video::class, $tag->videos->first());
    $this->assertEquals($video->id, $tag->videos->first()->id);
}

Conclusion

Unit testing your Eloquent relationships can be very useful. I hope you learned something from this tutorial. Thanks for reading!