diff --git a/src/product/AggregateNotFoundException.php b/src/product/AggregateNotFoundException.php
new file mode 100644
index 0000000..2d9c972
--- /dev/null
+++ b/src/product/AggregateNotFoundException.php
@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+use hiqdev\php\billing\Exception\RuntimeException;
+
+class AggregateNotFoundException extends RuntimeException
+{
+}
diff --git a/src/product/BehaviorCollection.php b/src/product/BehaviorCollection.php
new file mode 100644
index 0000000..bd548d7
--- /dev/null
+++ b/src/product/BehaviorCollection.php
@@ -0,0 +1,32 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+use hiqdev\billing\registry\Domain\Model\TariffType;
+
+class BehaviorCollection implements \IteratorAggregate
+{
+    /** @var BehaviorInterface[] */
+    private array $behaviors = [];
+
+    public function __construct(private readonly TariffType $tariffType)
+    {
+    }
+
+    /**
+     * @return BehaviorInterface[]
+     */
+    public function getIterator(): \Traversable
+    {
+        return new \ArrayIterator($this->behaviors);
+    }
+
+    public function attach(BehaviorInterface $behavior): self
+    {
+        $behavior->setTariffType($this->tariffType);
+
+        $this->behaviors[] = $behavior;
+
+        return $this;
+    }
+}
diff --git a/src/product/BehaviorInterface.php b/src/product/BehaviorInterface.php
new file mode 100644
index 0000000..36e054b
--- /dev/null
+++ b/src/product/BehaviorInterface.php
@@ -0,0 +1,15 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+use hiqdev\billing\registry\Domain\Model\TariffType;
+
+/**
+ * Empty interface for mark product behavior
+ */
+interface BehaviorInterface
+{
+    public function setTariffType(TariffType $tariffTypeName): void;
+
+    public function getTariffType(): TariffType;
+}
diff --git a/src/product/BehaviorNotFoundException.php b/src/product/BehaviorNotFoundException.php
new file mode 100644
index 0000000..efe6249
--- /dev/null
+++ b/src/product/BehaviorNotFoundException.php
@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+use hiqdev\php\billing\Exception\RuntimeException;
+
+class BehaviorNotFoundException extends RuntimeException
+{
+}
diff --git a/src/product/BillingRegistry.php b/src/product/BillingRegistry.php
new file mode 100644
index 0000000..7cbf6be
--- /dev/null
+++ b/src/product/BillingRegistry.php
@@ -0,0 +1,133 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+use hiqdev\billing\registry\invoice\RepresentationInterface;
+use hiqdev\billing\registry\product\Aggregate;
+use hiqdev\billing\registry\quantity\formatter\QuantityFormatterNotFoundException;
+use hiqdev\billing\registry\quantity\FractionQuantityData;
+use hiqdev\php\billing\type\Type;
+use hiqdev\php\billing\type\TypeInterface;
+
+class BillingRegistry implements BillingRegistryInterface
+{
+    /** @var TariffTypeDefinition[] */
+    private array $tariffTypes = [];
+    private bool $locked = false;
+
+    public function addTariffType(TariffTypeDefinition $tariffType): void
+    {
+        if ($this->locked) {
+            throw new \RuntimeException("BillingRegistry is locked and cannot be modified.");
+        }
+
+        $this->tariffTypes[] = $tariffType;
+    }
+
+    public function lock(): void
+    {
+        $this->locked = true;
+    }
+
+    public function priceTypes(): \Generator
+    {
+        foreach ($this->tariffTypes as $tariffType) {
+            foreach ($tariffType->withPrices() as $priceTypeDefinition) {
+                yield $priceTypeDefinition;
+            }
+        }
+    }
+
+    /**
+     * @param string $representationClass
+     * @return RepresentationInterface[]
+     */
+    public function getRepresentationsByType(string $representationClass): array
+    {
+        $representations = [];
+        foreach ($this->priceTypes() as $priceTypeDefinition) {
+            foreach ($priceTypeDefinition->documentRepresentation() as $representation) {
+                if ($representation instanceof $representationClass) {
+                    $representations[] = $representation;
+                }
+            }
+        }
+
+        return $representations;
+    }
+
+    public function createQuantityFormatter(
+        string $type,
+        FractionQuantityData $data,
+    ): array {
+        $type = $this->convertStringTypeToType($type);
+
+        foreach ($this->priceTypes() as $priceTypeDefinition) {
+            if ($priceTypeDefinition->hasType($type)) {
+                return $priceTypeDefinition->createQuantityFormatter($data);
+            }
+        }
+
+        throw new QuantityFormatterNotFoundException('Quantity formatter not found');
+    }
+
+    private function convertStringTypeToType(string $type): TypeInterface
+    {
+        return Type::anyId($type);
+    }
+
+    /**
+     * @param string $type - full type like 'overuse,lb_capacity_unit'
+     * @param string $behaviorClassWrapper
+     * @return BehaviorInterface
+     * @throws BehaviorNotFoundException
+     */
+    public function getBehavior(string $type, string $behaviorClassWrapper): BehaviorInterface
+    {
+        $type = $this->convertStringTypeToType($type);
+
+        foreach ($this->priceTypes() as $priceTypeDefinition) {
+            if ($priceTypeDefinition->hasType($type)) {
+                foreach ($priceTypeDefinition->withBehaviors() as $behavior) {
+                    if ($behavior instanceof $behaviorClassWrapper) {
+                        return $behavior;
+                    }
+                }
+            }
+        }
+
+        throw new BehaviorNotFoundException('Behaviour was not found');
+    }
+
+    public function getBehaviors(string $behaviorClassWrapper): \Generator
+    {
+        foreach ($this->tariffTypes as $tariffType) {
+            foreach ($tariffType->withBehaviors() as $behavior) {
+                if ($behavior instanceof $behaviorClassWrapper) {
+                    yield $behavior;
+                }
+            }
+        }
+
+        foreach ($this->priceTypes() as $priceTypeDefinition) {
+            foreach ($priceTypeDefinition->withBehaviors() as $behavior) {
+                if ($behavior instanceof $behaviorClassWrapper) {
+                    yield $behavior;
+                }
+            }
+        }
+    }
+
+    public function getAggregate(string $type): Aggregate
+    {
+        $type = $this->convertStringTypeToType($type);
+
+        foreach ($this->priceTypes() as $priceTypeDefinition) {
+            if ($priceTypeDefinition->hasType($type)) {
+                return $priceTypeDefinition->getAggregate();
+            }
+        }
+
+        throw new AggregateNotFoundException('Aggregate was not found');
+    }
+}
diff --git a/src/product/BillingRegistryInterface.php b/src/product/BillingRegistryInterface.php
new file mode 100644
index 0000000..ed4415b
--- /dev/null
+++ b/src/product/BillingRegistryInterface.php
@@ -0,0 +1,11 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+interface BillingRegistryInterface
+{
+    /**
+     * @return PriceTypeDefinition[]
+     */
+    public function priceTypes(): \Generator;
+}
\ No newline at end of file
diff --git a/src/product/DocumentRepresentationInterface.php b/src/product/DocumentRepresentationInterface.php
new file mode 100644
index 0000000..83b34fe
--- /dev/null
+++ b/src/product/DocumentRepresentationInterface.php
@@ -0,0 +1,8 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+interface DocumentRepresentationInterface
+{
+
+}
\ No newline at end of file
diff --git a/src/product/InvoiceDescriptionsBuilder.php b/src/product/InvoiceDescriptionsBuilder.php
new file mode 100644
index 0000000..5b5b720
--- /dev/null
+++ b/src/product/InvoiceDescriptionsBuilder.php
@@ -0,0 +1,23 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+class InvoiceDescriptionsBuilder
+{
+    private BillingRegistry $registry;
+
+    public function __construct(BillingRegistry $registry)
+    {
+        $this->registry = $registry;
+    }
+
+    public function build(): array
+    {
+        $descriptions = [];
+        foreach ($this->registry->priceTypes() as $priceType) {
+            $descriptions[] = $priceType->representInvoice();
+        }
+
+        return $descriptions;
+    }
+}
diff --git a/src/product/ParentNodeDefinitionInterface.php b/src/product/ParentNodeDefinitionInterface.php
new file mode 100644
index 0000000..ced0906
--- /dev/null
+++ b/src/product/ParentNodeDefinitionInterface.php
@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+interface ParentNodeDefinitionInterface
+{
+    public function withBehaviors(): BehaviorCollection;
+
+    public function hasBehavior(string $behaviorClassName): bool;
+}
\ No newline at end of file
diff --git a/src/product/PriceTypeDefinition.php b/src/product/PriceTypeDefinition.php
new file mode 100644
index 0000000..2e57126
--- /dev/null
+++ b/src/product/PriceTypeDefinition.php
@@ -0,0 +1,154 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+use hiqdev\billing\registry\behavior\PriceTypeDefinitionBehaviourCollection;
+use hiqdev\billing\registry\Domain\Model\TariffType;
+use hiqdev\billing\registry\Domain\Model\Unit\Unit;
+use hiqdev\billing\registry\invoice\InvoiceRepresentationCollection;
+use hiqdev\billing\registry\product\Aggregate;
+use hiqdev\billing\registry\quantity\formatter\QuantityFormatterDefinition;
+use hiqdev\billing\registry\quantity\formatter\QuantityFormatterFactory;
+use hiqdev\billing\registry\quantity\FractionQuantityData;
+use hiqdev\billing\registry\Domain\Model\Unit\FractionUnit;
+use hiqdev\php\billing\quantity\QuantityFormatterInterface;
+use hiqdev\php\billing\type\TypeInterface;
+
+class PriceTypeDefinition implements ParentNodeDefinitionInterface
+{
+    private Unit $unit;
+
+    private string $description;
+
+    private QuantityFormatterDefinition $quantityFormatterDefinition;
+
+    private InvoiceRepresentationCollection $invoiceCollection;
+
+    private PriceTypeDefinitionBehaviourCollection $behaviorCollection;
+
+    private Aggregate $aggregate;
+
+    public function __construct(
+        private readonly PriceTypeDefinitionCollection $parent,
+        private readonly TypeInterface $type,
+        TariffType $tariffType,
+    ) {
+        $this->invoiceCollection = new InvoiceRepresentationCollection($this);
+        $this->behaviorCollection = new PriceTypeDefinitionBehaviourCollection($this, $tariffType);
+
+        $this->init();
+    }
+
+    protected function init(): void
+    {
+        // Hook
+    }
+
+    public function unit(Unit $unit): self
+    {
+        $this->unit = $unit;
+
+        return $this;
+    }
+
+    public function description(string $description): self
+    {
+        $this->description = $description;
+
+        return $this;
+    }
+
+    public function getDescription(): string
+    {
+        return $this->description;
+    }
+
+    /**
+     * @param string $formatterClass
+     * @param null|FractionUnit|string $fractionUnit
+     * @return $this
+     */
+    public function quantityFormatter(string $formatterClass, $fractionUnit = null): self
+    {
+        // TODO: check if formatterClass exists
+        $this->quantityFormatterDefinition = new QuantityFormatterDefinition($formatterClass, $fractionUnit);
+
+        return $this;
+    }
+
+    public function createQuantityFormatter(
+        FractionQuantityData $data,
+    ): QuantityFormatterInterface {
+        return QuantityFormatterFactory::create(
+            $this->getUnit()->createExternalUnit(),
+            $this->quantityFormatterDefinition,
+            $data,
+        );
+    }
+
+    public function end(): PriceTypeDefinitionCollection
+    {
+        // Validate the PriceType and lock its state
+        return $this->parent;
+    }
+
+    public function documentRepresentation(): InvoiceRepresentationCollection
+    {
+        return $this->invoiceCollection;
+    }
+
+    public function measuredWith(\hiqdev\billing\registry\measure\RcpTrafCollector $param): self
+    {
+        return $this;
+    }
+
+    public function type(): TypeInterface
+    {
+        return $this->type;
+    }
+
+    public function hasType(TypeInterface $type): bool
+    {
+        return $this->type->equals($type);
+    }
+
+    public function getUnit(): Unit
+    {
+        return $this->unit;
+    }
+
+    public function withBehaviors(): PriceTypeDefinitionBehaviourCollection
+    {
+        return $this->behaviorCollection;
+    }
+
+    public function hasBehavior(string $behaviorClassName): bool
+    {
+        foreach ($this->behaviorCollection as $behavior) {
+            if ($behavior instanceof $behaviorClassName) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * це параметер визначає агрегатну функцію яка застосовується для щоденно записаних ресурсів щоб визнизначти
+     * місячне споживання за яке потрібно пробілити клієнта
+     *
+     * @param Aggregate $aggregate
+     * @return self
+     */
+    public function aggregation(Aggregate $aggregate): self
+    {
+        $this->aggregate = $aggregate;
+
+        return $this;
+    }
+
+    public function getAggregate(): Aggregate
+    {
+        return $this->aggregate;
+    }
+}
diff --git a/src/product/PriceTypeDefinitionCollection.php b/src/product/PriceTypeDefinitionCollection.php
new file mode 100644
index 0000000..f21fc76
--- /dev/null
+++ b/src/product/PriceTypeDefinitionCollection.php
@@ -0,0 +1,109 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+use hiqdev\billing\registry\Domain\Model\TariffType;
+use hiqdev\billing\registry\product\GType;
+use hiqdev\billing\registry\product\PriceType;
+use hiqdev\billing\registry\product\PriceTypeDefinition\PriceTypeDefinitionFactory;
+
+class PriceTypeDefinitionCollection implements \IteratorAggregate
+{
+    private array $pricesGroupedByPriceType = [];
+
+    public function __construct(private readonly TariffTypeDefinition $parent)
+    {
+    }
+
+    /**
+     * @return PriceTypeDefinition[]
+     */
+    public function getIterator(): \Traversable
+    {
+        return new \ArrayIterator($this->getAllPrices());
+    }
+
+    private function getAllPrices(): array
+    {
+        $allPrices = [];
+        foreach ($this->pricesGroupedByPriceType as $prices) {
+            foreach ($prices as $price) {
+                $allPrices[] = $price;
+            }
+        }
+
+        return $allPrices;
+    }
+
+    public function monthly(PriceType $type): PriceTypeDefinition
+    {
+        $priceType = $this->createPriceTypeDefinition(GType::monthly, $type, $this->parent->tariffType());
+
+        $this->addPriceTypeDefinition($type, $priceType);
+
+        return $priceType;
+    }
+
+    private function addPriceTypeDefinition(PriceType $type, PriceTypeDefinition $priceTypeDefinition): void
+    {
+        $this->pricesGroupedByPriceType[$type->name][] = $priceTypeDefinition;
+    }
+
+    private function createPriceTypeDefinition(
+        GType $gType,
+        PriceType $type,
+        TariffType $tariffType,
+    ): PriceTypeDefinition {
+        return PriceTypeDefinitionFactory::create($this, $type, $gType, $tariffType);
+    }
+
+    public function overuse(PriceType $type): PriceTypeDefinition
+    {
+        $priceType = $this->createPriceTypeDefinition(GType::overuse, $type, $this->parent->tariffType());
+
+        $this->addPriceTypeDefinition($type, $priceType);
+
+        return $priceType;
+    }
+
+    public function end(): TariffTypeDefinition
+    {
+        return $this->parent;
+    }
+
+    public function feature(PriceType $type): PriceTypeDefinition
+    {
+        $priceType = $this->createPriceTypeDefinition(GType::feature, $type, $this->parent->tariffType());
+
+        $this->addPriceTypeDefinition($type, $priceType);
+
+        return $priceType;
+    }
+
+    public function domain(PriceType $type): PriceTypeDefinition
+    {
+        $priceType = $this->createPriceTypeDefinition(GType::domain, $type, $this->parent->tariffType());
+
+        $this->addPriceTypeDefinition($type, $priceType);
+
+        return $priceType;
+    }
+
+    public function certificate(PriceType $type): PriceTypeDefinition
+    {
+        $priceType = $this->createPriceTypeDefinition(GType::certificate, $type, $this->parent->tariffType());
+
+        $this->addPriceTypeDefinition($type, $priceType);
+
+        return $priceType;
+    }
+
+    public function discount(PriceType $type): PriceTypeDefinition
+    {
+        $priceType = $this->createPriceTypeDefinition(GType::discount, $type, $this->parent->tariffType());
+
+        $this->addPriceTypeDefinition($type, $priceType);
+
+        return $priceType;
+    }
+}
diff --git a/src/product/ProductInterface.php b/src/product/ProductInterface.php
new file mode 100644
index 0000000..3b146fd
--- /dev/null
+++ b/src/product/ProductInterface.php
@@ -0,0 +1,8 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+interface ProductInterface
+{
+    public function name(): string;
+}
\ No newline at end of file
diff --git a/src/product/ServerProduct.php b/src/product/ServerProduct.php
new file mode 100644
index 0000000..5d8fbef
--- /dev/null
+++ b/src/product/ServerProduct.php
@@ -0,0 +1,11 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+class ServerProduct implements ProductInterface
+{
+    public function name(): string
+    {
+        // TODO: Implement name() method.
+    }
+}
diff --git a/src/product/TariffTypeDefinition.php b/src/product/TariffTypeDefinition.php
new file mode 100644
index 0000000..260b4d7
--- /dev/null
+++ b/src/product/TariffTypeDefinition.php
@@ -0,0 +1,67 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\product;
+
+use hiqdev\billing\registry\behavior\TariffTypeBehaviorCollection;
+use hiqdev\billing\registry\product\Product;
+use hiqdev\billing\registry\Domain\Model\TariffType;
+
+class TariffTypeDefinition implements ParentNodeDefinitionInterface
+{
+    private Product $product;
+
+    private PriceTypeDefinitionCollection $prices;
+
+    private TariffTypeBehaviorCollection $behaviorCollection;
+
+    public function __construct(private readonly TariffType $tariffType)
+    {
+        $this->prices = new PriceTypeDefinitionCollection($this);
+        $this->behaviorCollection = new TariffTypeBehaviorCollection($this, $tariffType);
+    }
+
+    public function tariffType(): TariffType
+    {
+        return $this->tariffType;
+    }
+
+    public function ofProduct(Product $product): self
+    {
+        $this->product = $product;
+
+        return $this;
+    }
+
+    public function setPricesSuggester(string $suggesterClass): self
+    {
+        // Validate or store the suggester class
+        return $this;
+    }
+
+    public function withPrices(): PriceTypeDefinitionCollection
+    {
+        return $this->prices;
+    }
+
+    public function withBehaviors(): TariffTypeBehaviorCollection
+    {
+        return $this->behaviorCollection;
+    }
+
+    public function hasBehavior(string $behaviorClassName): bool
+    {
+        foreach ($this->behaviorCollection as $behavior) {
+            if ($behavior instanceof $behaviorClassName) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    public function end(): self
+    {
+        // Validate the TariffType and lock its state
+        return $this;
+    }
+}
diff --git a/src/quantity/QuantityFormatterInterface.php b/src/quantity/QuantityFormatterInterface.php
new file mode 100644
index 0000000..4f8c322
--- /dev/null
+++ b/src/quantity/QuantityFormatterInterface.php
@@ -0,0 +1,28 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\quantity;
+
+interface QuantityFormatterInterface
+{
+    /**
+     * Returns textual user friendly representation of the quantity.
+     * E.g. 20 days, 30 GB, 1 year.
+     *
+     * @return string
+     */
+    public function format(): string;
+
+    /**
+     * Returns numeric to be saved in DB.
+     *
+     * @return string
+     */
+    public function getValue(): string;
+
+    /**
+     * Returns numeric user friendly representation of the quantity.
+     *
+     * @return string
+     */
+    public function getClientValue(): string;
+}
\ No newline at end of file
diff --git a/tests/unit/product/InvoiceDescriptionsBuilderTest.php b/tests/unit/product/InvoiceDescriptionsBuilderTest.php
new file mode 100644
index 0000000..01670b2
--- /dev/null
+++ b/tests/unit/product/InvoiceDescriptionsBuilderTest.php
@@ -0,0 +1,69 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\tests\unit\product;
+
+use hiqdev\billing\registry\invoice\InvoiceRepresentation;
+use hiqdev\billing\registry\invoice\PaymentRequestRepresentation;
+use hiqdev\billing\registry\product\ServerProduct;
+use PHPUnit\Framework\TestCase;
+
+class InvoiceDescriptionsBuilderTest extends TestCase
+{
+    public function testInvoiceDescriptionsBuilderWithRealClasses()
+    {
+        // Create TariffType with real prices and behaviors
+        $serverTariffType = (new TariffType('server'))
+            ->ofProduct(ServerProduct::class)
+            ->setPricesSuggester(\hiapi\legacy\lib\billing\price\suggester\device\ServerPricesSuggester::class)
+            ->withPrices()
+                ->monthly('support_time')
+                    ->unit('hour')
+                    ->description('Monthly fee for support time')
+                    ->quantityFormatter(MonthlyQuantityFormatter::class)
+                    ->invoiceRepresentation(function () {
+                        return 'Invoice for support_time (monthly): $100';
+                    })
+                    ->documentRepresentation()
+                        ->attach(new InvoiceRepresentation("trunc(quantity::numeric,0)||' of '||trunc(maxquantity::numeric,0)||' Anycast IP-addresses in '||period"))
+                        ->attach(new PaymentRequestRepresentation("'Recommended prepayment '||trunc(quantity::numeric,0)||' of '||trunc(maxquantity::numeric,0)||' Anycast IP-addresses in '||period"))
+                    ->end()
+                ->end()
+                ->overuse('support_time')
+                    ->unit('hour')
+                    ->description('Support time overuse')
+                    ->quantityFormatter(HourBasedOveruseQuantityFormatter::class)
+                    ->invoiceRepresentation(function () {
+                        return 'Invoice for support_time (overuse): $50';
+                    })
+                ->end()
+            ->end()  // Returns control to TariffType
+            ->withBehaviors()
+            ->attach(new OncePerMonthPlanChangeBehavior())
+            ->end();
+
+        // Create BillingRegistry and add the TariffType
+        $billingRegistry = new BillingRegistry();
+        $billingRegistry->addTariffType($serverTariffType);
+        $billingRegistry->lock();
+
+        // Build invoice descriptions
+        $builder = new InvoiceDescriptionsBuilder($billingRegistry);
+        $invoiceDescriptions = $builder->build();
+
+        // Verify the results
+        $this->assertIsArray($invoiceDescriptions, 'build() should return an array of invoice descriptions.');
+        $this->assertCount(2, $invoiceDescriptions, 'There should be 2 invoice descriptions generated.');
+
+        $this->assertSame(
+            'Invoice for support_time (monthly): $100',
+            $invoiceDescriptions[0],
+            'The first description should match the expected monthly invoice description.'
+        );
+
+        $this->assertSame(
+            'Invoice for support_time (overuse): $50',
+            $invoiceDescriptions[1],
+            'The second description should match the expected overuse invoice description.'
+        );
+    }
+}
diff --git a/tests/unit/product/TariffTypeTest.php b/tests/unit/product/TariffTypeTest.php
new file mode 100644
index 0000000..dd04751
--- /dev/null
+++ b/tests/unit/product/TariffTypeTest.php
@@ -0,0 +1,77 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\tests\unit\product;
+
+use hiqdev\php\billing\product\PriceTypesCollection;
+use hiqdev\php\billing\product\TariffType;
+use PHPUnit\Framework\TestCase;
+
+class TariffTypeTest extends TestCase
+{
+    public function testTariffTypeInitialization(): void
+    {
+        $tariffType = new TariffType('server');
+
+        $this->assertSame('server', $this->getPrivateProperty($tariffType, 'name'), 'TariffType name should be initialized correctly.');
+        $this->assertInstanceOf(PriceTypesCollection::class, $this->getPrivateProperty($tariffType, 'prices'), 'Prices should be an instance of PriceTypesCollection.');
+    }
+
+    public function testOfProduct(): void
+    {
+        $tariffType = new TariffType('server');
+        $tariffType->ofProduct('ServerProductClass');
+
+        $this->assertSame(
+            'ServerProductClass',
+            $this->getPrivateProperty($tariffType, 'productClass'),
+            'Product class should be set correctly.'
+        );
+    }
+
+    public function testAttachBehavior(): void
+    {
+        $tariffType = new TariffType('server');
+        $behavior = new OncePerMonthPlanChangeBehavior();
+        $tariffType->attach($behavior);
+
+        $behaviors = $this->getPrivateProperty($tariffType, 'behaviors');
+
+        $this->assertCount(1, $behaviors, 'Behavior should be added to the behaviors list.');
+        $this->assertSame($behavior, $behaviors[0], 'Behavior should match the attached instance.');
+    }
+
+    public function testPricesCollectionInteraction(): void
+    {
+        $tariffType = new TariffType('server');
+        $prices = $tariffType->withPrices();
+
+        $this->assertInstanceOf(PriceTypesCollection::class, $prices, 'withPrices() should return a PriceTypesCollection instance.');
+
+        $priceType = $prices->monthly('support_time');
+        $priceType->unit('hour')->description('Monthly fee for support time');
+        $priceType->end();
+
+        $this->assertNotEmpty($this->getPrivateProperty($prices, 'prices'), 'PriceTypesCollection should contain defined price types.');
+    }
+
+    public function testEndLocksTariffType(): void
+    {
+        $tariffType = new TariffType('server');
+        $tariffType->end();
+
+        // Assuming TariffType has a `locked` private property
+        $isLocked = $this->getPrivateProperty($tariffType, 'locked');
+        $this->assertTrue($isLocked, 'TariffType should be locked after calling end().');
+    }
+
+    /**
+     * Helper function to access private properties for testing.
+     */
+    private function getPrivateProperty($object, $propertyName)
+    {
+        $reflection = new \ReflectionClass($object);
+        $property = $reflection->getProperty($propertyName);
+        $property->setAccessible(true);
+        return $property->getValue($object);
+    }
+}