diff --git a/composer.json b/composer.json
index cbb1979..3833ddd 100644
--- a/composer.json
+++ b/composer.json
@@ -36,7 +36,7 @@
     },
     "scripts": {
         "test": "vendor/bin/pest",
-            "test-coverage": "vendor/bin/pest --coverage",
+        "test-coverage": "vendor/bin/pest --coverage",
         "format": "vendor/bin/pint"
     },
     "config": {
diff --git a/src/Abstracts/Resource.php b/src/Abstracts/Resource.php
index fcf06a9..523f10e 100644
--- a/src/Abstracts/Resource.php
+++ b/src/Abstracts/Resource.php
@@ -15,7 +15,7 @@ abstract class Resource
 {
     public string $self;
 
-    public function __construct(array|string|int|float $properties = null)
+    public function __construct(array|string|int|float|null $properties = null)
     {
         if (is_array($properties)) {
             $this->populate($properties);
@@ -43,8 +43,15 @@ protected function resolvePropertyValue(string $property, mixed $value): mixed
 
         $propertyReflection = $reflection->getProperty($property);
 
+        $reflectionTypeName = $propertyReflection->getType()->getName();
+
+        // If is already the expected type
+        if ($value instanceof $reflectionTypeName) {
+            return $value;
+        }
+
         // If is EconomicCollection
-        if (is_a($propertyReflection->getType()->getName(), EconomicCollection::class, true)) {
+        if (is_a($reflectionTypeName, EconomicCollection::class, true)) {
             $attribute = $propertyReflection->getAttributes(ResourceType::class);
 
             if (! empty($attribute[0])) {
@@ -55,7 +62,7 @@ protected function resolvePropertyValue(string $property, mixed $value): mixed
         }
 
         // If is a class
-        if (class_exists($propertyReflection->getType()->getName())) {
+        if (class_exists($reflectionTypeName)) {
             return new ($propertyReflection->getType()->getName())($value);
         }
 
@@ -151,4 +158,19 @@ public function __toString(): string
     {
         return json_encode($this->toArray());
     }
+
+    protected static function filterEmpty(array $values): array
+    {
+        foreach ($values as $key => $value) {
+            if (is_array($value)) {
+                $values[$key] = static::filterEmpty($value);
+            }
+
+            if (empty($values[$key])) {
+                unset($values[$key]);
+            }
+        }
+
+        return $values;
+    }
 }
diff --git a/src/Classes/EconomicQueryBuilder.php b/src/Classes/EconomicQueryBuilder.php
index d4c22b7..17b29e7 100644
--- a/src/Classes/EconomicQueryBuilder.php
+++ b/src/Classes/EconomicQueryBuilder.php
@@ -42,7 +42,7 @@ protected function getEndpoint(): string
         return $this->endpoint;
     }
 
-    public function where(int|string|Closure $propertyName, string $operatorOrValue = null, mixed $value = null): static
+    public function where(int|string|Closure $propertyName, ?string $operatorOrValue = null, mixed $value = null): static
     {
         if (! isset($this->filter)) {
             $this->filter = new EconomicQueryFilterBuilder(EconomicQueryFilterBuilder::FILTER_RELATION_AND);
@@ -53,7 +53,7 @@ public function where(int|string|Closure $propertyName, string $operatorOrValue
         return $this;
     }
 
-    public function orWhere(int|string|Closure $propertyName, string $operatorOrValue = null, mixed $value = null): static
+    public function orWhere(int|string|Closure $propertyName, ?string $operatorOrValue = null, mixed $value = null): static
     {
         if (! isset($this->filter)) {
             $this->filter = new EconomicQueryFilterBuilder(EconomicQueryFilterBuilder::FILTER_RELATION_OR);
diff --git a/src/Classes/EconomicQueryFilterBuilder.php b/src/Classes/EconomicQueryFilterBuilder.php
index 3191a32..4ba7fd1 100644
--- a/src/Classes/EconomicQueryFilterBuilder.php
+++ b/src/Classes/EconomicQueryFilterBuilder.php
@@ -73,7 +73,7 @@ protected function whereNested(Closure $closure)
         return $this;
     }
 
-    public function where(int|string|Closure $propertyName, string $operatorOrValue = null, mixed $value = null): static
+    public function where(int|string|Closure $propertyName, ?string $operatorOrValue = null, mixed $value = null): static
     {
         if ($propertyName instanceof Closure) {
             return $this->whereNested($propertyName);
@@ -91,7 +91,7 @@ public function where(int|string|Closure $propertyName, string $operatorOrValue
         return $this;
     }
 
-    public function orWhere(int|string|Closure $propertyName, string $operatorOrValue = null, mixed $value = null): static
+    public function orWhere(int|string|Closure $propertyName, ?string $operatorOrValue = null, mixed $value = null): static
     {
         $instance = new static(static::FILTER_RELATION_OR);
 
diff --git a/src/DTOs/Attention.php b/src/DTOs/Attention.php
new file mode 100644
index 0000000..2a22535
--- /dev/null
+++ b/src/DTOs/Attention.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace MorningTrain\Economic\DTOs;
+
+class Attention
+{
+    public function __construct(
+        public ?int $customerContactNumber = null,
+    ) {
+    }
+}
diff --git a/src/DTOs/Recipient.php b/src/DTOs/Recipient.php
new file mode 100644
index 0000000..0d0e233
--- /dev/null
+++ b/src/DTOs/Recipient.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace MorningTrain\Economic\DTOs;
+
+use MorningTrain\Economic\Resources\VatZone;
+
+class Recipient
+{
+    public function __construct(
+        public readonly string $name,
+        public readonly VatZone $vatZone,
+        public ?string $address = null,
+        public ?string $zip = null,
+        public ?string $city = null,
+        public ?string $country = null,
+        public ?string $ean = null,
+        public ?string $publicEntryNumber = null,
+        //public ?Attention $attention = null,
+    ) {
+    }
+}
diff --git a/src/Resources/Customer.php b/src/Resources/Customer.php
index 498230f..2cfa566 100644
--- a/src/Resources/Customer.php
+++ b/src/Resources/Customer.php
@@ -107,25 +107,25 @@ public static function create(
         Currency|string $currency,
         VatZone|int $vatZone,
         PaymentTerm|int $paymentTerms,
-        string $email = null,
-        string $address = null,
-        string $zip = null,
-        string $city = null,
-        string $country = null,
-        string $corporateIdentificationNumber = null,
-        string $pNumber = null,
-        string $vatNumber = null,
-        string $ean = null,
-        string $publicEntryNumber = null,
-        string $website = null,
-        string $mobilePhone = null,
-        string $telephoneAndFaxNumber = null,
-        bool $barred = null,
-        bool $eInvoicingDisabledByDefault = null,
-        float $creditLimit = null,
-        int $customerNumber = null,
-        Layout|int $layout = null,
-        Employee|int $salesPerson = null,
+        ?string $email = null,
+        ?string $address = null,
+        ?string $zip = null,
+        ?string $city = null,
+        ?string $country = null,
+        ?string $corporateIdentificationNumber = null,
+        ?string $pNumber = null,
+        ?string $vatNumber = null,
+        ?string $ean = null,
+        ?string $publicEntryNumber = null,
+        ?string $website = null,
+        ?string $mobilePhone = null,
+        ?string $telephoneAndFaxNumber = null,
+        ?bool $barred = null,
+        ?bool $eInvoicingDisabledByDefault = null,
+        ?float $creditLimit = null,
+        ?int $customerNumber = null,
+        Layout|int|null $layout = null,
+        Employee|int|null $salesPerson = null,
     ): static {
         return static::createRequest(array_filter(compact(
             'name',
diff --git a/src/Resources/Customer/Contact.php b/src/Resources/Customer/Contact.php
index a70defe..1b545f9 100644
--- a/src/Resources/Customer/Contact.php
+++ b/src/Resources/Customer/Contact.php
@@ -55,11 +55,11 @@ public static function fromCustomer(Customer|int $customer)
     public static function create(
         Customer $customer,
         string $name,
-        string $email = null,
-        string $phone = null,
-        string $notes = null,
-        string $eInvoiceId = null,
-        array $emailNotifications = null
+        ?string $email = null,
+        ?string $phone = null,
+        ?string $notes = null,
+        ?string $eInvoiceId = null,
+        ?array $emailNotifications = null
     ) {
         return static::createRequest(array_filter(compact(
             'customer',
diff --git a/src/Resources/Invoice.php b/src/Resources/Invoice.php
deleted file mode 100644
index f8bc95f..0000000
--- a/src/Resources/Invoice.php
+++ /dev/null
@@ -1,27 +0,0 @@
-<?php
-
-namespace MorningTrain\Economic\Resources;
-
-use MorningTrain\Economic\Abstracts\Resource;
-use MorningTrain\Economic\Resources\Invoice\ProductLine;
-
-class Invoice extends Resource
-{
-    public static function new(
-        Customer|int $customer,
-        Layout|int $layout,
-        Currency|string $currency,
-        PaymentTerm|int $paymentTerms
-    ) {
-        return new static([
-            'customer' => $customer,
-            'layout' => $layout,
-            'currency' => $currency,
-            'paymentTerms' => $paymentTerms,
-        ]);
-    }
-
-    public function addLine(ProductLine $line)
-    {
-    }
-}
diff --git a/src/Resources/Invoice/BookedInvoice.php b/src/Resources/Invoice/BookedInvoice.php
new file mode 100644
index 0000000..2d8e56b
--- /dev/null
+++ b/src/Resources/Invoice/BookedInvoice.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace MorningTrain\Economic\Resources\Invoice;
+
+use MorningTrain\Economic\Attributes\Resources\Create;
+use MorningTrain\Economic\Attributes\Resources\GetCollection;
+use MorningTrain\Economic\Attributes\Resources\GetSingle;
+
+#[GetCollection('invoices/booked')]
+#[GetSingle('invoices/booked/:bookedInvoiceNumber', ':bookedInvoiceNumber')]
+#[Create('invoices/booked')]
+class BookedInvoice extends DraftInvoice
+{
+    public static function createFromDraft(int|DraftInvoice $draft)
+    {
+        return static::createRequest([
+            'draftInvoice' => [
+                'draftInvoiceNumber' => is_int($draft) ? $draft : $draft->draftInvoiceNumber,
+            ],
+        ]);
+    }
+}
diff --git a/src/Resources/Invoice/DraftInvoice.php b/src/Resources/Invoice/DraftInvoice.php
new file mode 100644
index 0000000..9e3ada6
--- /dev/null
+++ b/src/Resources/Invoice/DraftInvoice.php
@@ -0,0 +1,77 @@
+<?php
+
+namespace MorningTrain\Economic\Resources\Invoice;
+
+use DateTime;
+use MorningTrain\Economic\Abstracts\Resource;
+use MorningTrain\Economic\Attributes\Resources\Create;
+use MorningTrain\Economic\Attributes\Resources\GetCollection;
+use MorningTrain\Economic\Attributes\Resources\GetSingle;
+use MorningTrain\Economic\DTOs\Recipient;
+use MorningTrain\Economic\Resources\Currency;
+use MorningTrain\Economic\Resources\Customer;
+use MorningTrain\Economic\Resources\Layout;
+use MorningTrain\Economic\Resources\PaymentTerm;
+use MorningTrain\Economic\Traits\Resources\Creatable;
+use MorningTrain\Economic\Traits\Resources\GetCollectionable;
+use MorningTrain\Economic\Traits\Resources\GetSingleable;
+use MorningTrain\Economic\Traits\Resources\HasLines;
+
+#[GetCollection('invoices/drafts')]
+#[GetSingle('invoices/drafts/:draftInvoiceNumber', ':draftInvoiceNumber')]
+#[Create('invoices/drafts')]
+class DraftInvoice extends Resource
+{
+    use Creatable, GetCollectionable, GetSingleable;
+    use HasLines;
+
+    public Customer $customer;
+
+    public Layout $layout;
+
+    public Currency $currency;
+
+    public PaymentTerm $paymentTerms;
+
+    public DateTime $date;
+
+    public Recipient $recipient;
+
+    public ?int $draftInvoiceNumber = null;
+
+    public static function new(
+        Customer|int $customer,
+        Layout|int $layout,
+        Currency|string $currency,
+        PaymentTerm|int $paymentTerms,
+        DateTime $date,
+        Recipient $recipient,
+    ): static {
+        return new static([
+            'customer' => $customer,
+            'layout' => $layout,
+            'currency' => $currency,
+            'paymentTerms' => $paymentTerms,
+            'date' => $date,
+            'recipient' => $recipient,
+        ]);
+    }
+
+    public function create()
+    {
+        return static::createRequest([
+            'customer' => $this->customer,
+            'layout' => $this->layout,
+            'currency' => $this->currency,
+            'paymentTerms' => $this->paymentTerms,
+            'date' => $this->date->format('Y-m-d'),
+            'recipient' => $this->recipient,
+            'lines' => $this->lines ?? null,
+        ]);
+    }
+
+    public function book(): ?BookedInvoice
+    {
+        return BookedInvoice::createFromDraft($this);
+    }
+}
diff --git a/src/Resources/Invoice/Invoice.php b/src/Resources/Invoice/Invoice.php
new file mode 100644
index 0000000..c981cf6
--- /dev/null
+++ b/src/Resources/Invoice/Invoice.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace MorningTrain\Economic\Resources\Invoice;
+
+use MorningTrain\Economic\Abstracts\Resource;
+use MorningTrain\Economic\Attributes\Resources\Create;
+use MorningTrain\Economic\Attributes\Resources\GetCollection;
+use MorningTrain\Economic\Attributes\Resources\GetSingle;
+use MorningTrain\Economic\Resources\Currency;
+use MorningTrain\Economic\Resources\Customer;
+use MorningTrain\Economic\Resources\Layout;
+use MorningTrain\Economic\Resources\PaymentTerm;
+use MorningTrain\Economic\Traits\Resources\Creatable;
+use MorningTrain\Economic\Traits\Resources\GetCollectionable;
+use MorningTrain\Economic\Traits\Resources\GetSingleable;
+
+#[GetCollection('products')]
+#[GetSingle('invoices/:product', ':product')]
+#[Create('invoices/drafts')]
+class Invoice extends Resource
+{
+    use Creatable, GetCollectionable, GetSingleable;
+
+    public static function new(
+        Customer|int $customer,
+        Layout|int $layout,
+        Currency|string $currency,
+        PaymentTerm|int $paymentTerms,
+    ) {
+        return new static([
+            'customer' => $customer,
+            'layout' => $layout,
+            'currency' => $currency,
+            'paymentTerms' => $paymentTerms,
+        ]);
+    }
+
+    public function addLine(ProductLine $line): static
+    {
+        $this->lines[] = $line;
+
+        return $this;
+    }
+}
diff --git a/src/Resources/Invoice/ProductLine.php b/src/Resources/Invoice/ProductLine.php
index 656ee8e..5b4ecf2 100644
--- a/src/Resources/Invoice/ProductLine.php
+++ b/src/Resources/Invoice/ProductLine.php
@@ -3,7 +3,41 @@
 namespace MorningTrain\Economic\Resources\Invoice;
 
 use MorningTrain\Economic\Abstracts\Resource;
+use MorningTrain\Economic\Resources\Product;
 
 class ProductLine extends Resource
 {
+    public ?string $description;
+    public ?float $discountPercentage;
+    public ?float $marginInBaseCurrency;
+    public ?float $marginPercentage;
+    public ?Product $product;
+    public ?float $quantity;
+    public ?int $sortKey;
+    public ?float $unitCostPrice;
+    public ?float $unitNetPrice;
+
+    public static function new(
+        Product|int $product,
+        float $quantity,
+        float $unitNetPrice,
+        string $description = null,
+        float $discountPercentage = null,
+        float $marginInBaseCurrency = null,
+        float $marginPercentage = null,
+        int $sortKey = null,
+        float $unitCostPrice = null,
+    ): static {
+        return new static([
+            'product' => $product,
+            'quantity' => $quantity,
+            'unitNetPrice' => $unitNetPrice,
+            'description' => $description,
+            'discountPercentage' => $discountPercentage,
+            'marginInBaseCurrency' => $marginInBaseCurrency,
+            'marginPercentage' => $marginPercentage,
+            'sortKey' => $sortKey,
+            'unitCostPrice' => $unitCostPrice,
+        ]);
+    }
 }
diff --git a/src/Resources/Layout.php b/src/Resources/Layout.php
index 0134907..bedd5fd 100644
--- a/src/Resources/Layout.php
+++ b/src/Resources/Layout.php
@@ -5,13 +5,20 @@
 use MorningTrain\Economic\Abstracts\Resource;
 use MorningTrain\Economic\Attributes\Resources\GetCollection;
 use MorningTrain\Economic\Attributes\Resources\GetSingle;
+use MorningTrain\Economic\Attributes\Resources\Properties\PrimaryKey;
+use MorningTrain\Economic\Traits\Resources\GetCollectionable;
+use MorningTrain\Economic\Traits\Resources\GetSingleable;
 
 #[GetCollection('layouts')]
 #[GetSingle('/layouts/:layoutNumber', ':layoutNumber')]
 class Layout extends Resource
 {
+    use GetCollectionable;
+    use GetSingleable;
+
     public bool $deleted;
 
+    #[PrimaryKey]
     public int $layoutNumber;
 
     public string $name;
diff --git a/src/Resources/PaymentTerm.php b/src/Resources/PaymentTerm.php
index c598965..3b5eb15 100644
--- a/src/Resources/PaymentTerm.php
+++ b/src/Resources/PaymentTerm.php
@@ -53,7 +53,7 @@ class PaymentTerm extends Resource
     public string $name;
 
     #[PrimaryKey]
-    public int $paymentTermNumber;
+    public int $paymentTermsNumber;
 
     public string $paymentTermsType;
 
diff --git a/src/Services/EconomicLoggerService.php b/src/Services/EconomicLoggerService.php
index 01ab159..36707a2 100644
--- a/src/Services/EconomicLoggerService.php
+++ b/src/Services/EconomicLoggerService.php
@@ -9,7 +9,7 @@ class EconomicLoggerService
 {
     protected static array $loggers = [];
 
-    public static function registerLogger(LoggerInterface $logger, string|array $logLevels = null): void
+    public static function registerLogger(LoggerInterface $logger, string|array|null $logLevels = null): void
     {
         if ($logLevels === null) {
             static::$loggers['all'][] = $logger;
diff --git a/src/Traits/Resources/Creatable.php b/src/Traits/Resources/Creatable.php
index 72ea238..4d9d703 100644
--- a/src/Traits/Resources/Creatable.php
+++ b/src/Traits/Resources/Creatable.php
@@ -16,16 +16,23 @@ public static function createRequest($args, array $endpointReferences = []): ?st
     {
         // TODO: add validation method to check if required properties are set and primary key is not set - throw exception if not
 
+        $args = json_decode(json_encode($args), true);
+
+        if (method_exists(static::class, 'filterEmpty')) {
+            $args = static::filterEmpty($args);
+        }
+
         $response = EconomicApiService::post(static::getEndpoint(Create::class, ...$endpointReferences), $args);
 
         if ($response->getStatusCode() !== 201) {
-            EconomicLoggerService::error('Economic API Service returned a non 201 status code when creating a resource', [
-                'status_code' => $response->getStatusCode(),
-                'response_body' => $response->getBody(),
-                'resource' => static::class,
-                'args' => $args,
-                'endpoint_references' => $endpointReferences,
-            ]);
+            EconomicLoggerService::error('Economic API Service returned a non 201 status code when creating a resource',
+                [
+                    'status_code' => $response->getStatusCode(),
+                    'response_body' => $response->getBody(),
+                    'resource' => static::class,
+                    'args' => $args,
+                    'endpoint_references' => $endpointReferences,
+                ]);
 
             throw new Exception('Economic API Service returned a non 201 status code when creating a resource');
         }
diff --git a/src/Traits/Resources/HasLines.php b/src/Traits/Resources/HasLines.php
new file mode 100644
index 0000000..418f1f7
--- /dev/null
+++ b/src/Traits/Resources/HasLines.php
@@ -0,0 +1,20 @@
+<?php
+
+namespace MorningTrain\Economic\Traits\Resources;
+
+use MorningTrain\Economic\Resources\Invoice\ProductLine;
+
+trait HasLines
+{
+    /**
+     * @var array ProductLine[]
+     */
+    public array $lines = [];
+
+    public function addLine(ProductLine $line): static
+    {
+        $this->lines[] = $line;
+
+        return $this;
+    }
+}
diff --git a/tests/DummyEconomicDriver.php b/tests/DummyEconomicDriver.php
index 71acc64..e0eaf7e 100644
--- a/tests/DummyEconomicDriver.php
+++ b/tests/DummyEconomicDriver.php
@@ -20,25 +20,30 @@ public function __construct(string $appSecretToken, string $agreementGrantToken)
     public function get(string $url, array $queryArgs = []): EconomicResponse
     {
         // TODO: Implement get() method.
+        ray(func_get_args());
     }
 
     public function post(string $url, array $body = []): EconomicResponse
     {
         // TODO: Implement post() method.
+        ray(func_get_args());
     }
 
     public function put(string $url, array $body = []): EconomicResponse
     {
         // TODO: Implement put() method.
+        ray(func_get_args());
     }
 
     public function delete(string $url): EconomicResponse
     {
         // TODO: Implement delete() method.
+        ray(func_get_args());
     }
 
     public function patch(string $url): EconomicResponse
     {
         // TODO: Implement patch() method.
+        ray(func_get_args());
     }
 }
diff --git a/tests/Unit/InvoiceTest.php b/tests/Unit/InvoiceTest.php
new file mode 100644
index 0000000..aa4c177
--- /dev/null
+++ b/tests/Unit/InvoiceTest.php
@@ -0,0 +1,146 @@
+<?php
+
+use MorningTrain\Economic\Classes\EconomicResponse;
+use MorningTrain\Economic\DTOs\Recipient;
+use MorningTrain\Economic\Resources\Invoice\DraftInvoice;
+use MorningTrain\Economic\Resources\Invoice\ProductLine;
+use MorningTrain\Economic\Resources\Product;
+use MorningTrain\Economic\Resources\VatZone;
+
+it('creates draft invoice', function () {
+    $this->driver->expects()->post()
+        ->withArgs(function (string $url, array $body) {
+            return $url === 'https://restapi.e-conomic.com/invoices/drafts'
+                && $body === [
+                    'customer' => [
+                        'customerNumber' => 1,
+                    ],
+                    'layout' => [
+                        'layoutNumber' => 1,
+                    ],
+                    'currency' => [
+                        'isoNumber' => 'DKK',
+                    ],
+                    'paymentTerms' => [
+                        'paymentTermsNumber' => 1,
+                    ],
+                    'date' => '2021-01-01',
+                    'recipient' => [
+                        'name' => 'John Doe',
+                        'vatZone' => [
+                            'vatZoneNumber' => 1,
+                        ],
+                    ],
+                    'lines' => [
+                        [
+                            'quantity' => 1,
+                            'unitNetPrice' => 500,
+                        ],
+                    ],
+                ];
+        })
+        ->once()
+        ->andReturn(new EconomicResponse(201, []));
+
+    DraftInvoice::new(
+        1,
+        1,
+        'DKK',
+        1,
+        DateTime::createFromFormat('Y-m-d', '2021-01-01'),
+        new Recipient(
+            'John Doe',
+            new VatZone(1),
+        )
+    )
+        ->addLine(ProductLine::new(
+            product: new Product(1),
+            quantity: 1,
+            unitNetPrice: 500
+        ))
+        ->create();
+});
+
+it('books draft invoice', function () {
+    $this->driver->expects()->post()
+        ->withArgs(function (string $url, array $body) {
+            return $url === 'https://restapi.e-conomic.com/invoices/drafts';
+        })
+        ->once()
+        ->andReturn(new EconomicResponse(201, [
+            'draftInvoiceNumber' => 1,
+        ]));
+
+    $this->driver->expects()->post()
+        ->withArgs(function (string $url, array $body) {
+            return $url === 'https://restapi.e-conomic.com/invoices/booked'
+                && $body === [
+                    'draftInvoice' => [
+                        'draftInvoiceNumber' => 1,
+                    ],
+                ];
+        })
+        ->once()
+        ->andReturn(new EconomicResponse(201, []));
+
+    DraftInvoice::new(
+        1,
+        1,
+        'DKK',
+        1,
+        DateTime::createFromFormat('Y-m-d', '2021-01-01'),
+        new Recipient(
+            'John Doe',
+            new VatZone(1),
+        )
+    )
+        ->create()
+        ->book();
+});
+
+it('can add lines', function () {
+    $invoice = DraftInvoice::new(
+        1,
+        1,
+        'DKK',
+        1,
+        DateTime::createFromFormat('Y-m-d', '2021-01-01'),
+        new Recipient(
+            'John Doe',
+            new VatZone(1),
+        )
+    )
+        ->addLine(ProductLine::new(
+            product: new Product(1),
+            quantity: 1,
+            unitNetPrice: 500
+        ))
+        ->addLine(ProductLine::new(
+            product: new Product(2),
+            quantity: 5,
+            unitNetPrice: 100,
+            description: 'Some description',
+        ));
+
+    expect($invoice->lines)
+        ->toBeArray()
+        ->toHaveCount(2);
+
+    expect($invoice->lines[0])
+        ->toBeInstanceOf(ProductLine::class)
+        ->description->toBeNull()
+        ->discountPercentage->toBeNull()
+        ->marginInBaseCurrency->toBeNull()
+        ->marginPercentage->toBeNull()
+        ->product->toBeInstanceOf(Product::class)
+        ->quantity->toBe(1.0);
+
+    expect($invoice->lines[1])
+        ->toBeInstanceOf(ProductLine::class)
+        ->description->toBe('Some description')
+        ->discountPercentage->toBeNull()
+        ->marginInBaseCurrency->toBeNull()
+        ->marginPercentage->toBeNull()
+        ->product->toBeInstanceOf(Product::class)
+        ->quantity->toBe(5.0);
+});