diff --git a/tests/Gateways/Contract/GatewayContractTestCase.php b/tests/Gateways/Contract/GatewayContractTestCase.php
new file mode 100644
index 0000000..12a4446
--- /dev/null
+++ b/tests/Gateways/Contract/GatewayContractTestCase.php
@@ -0,0 +1,128 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Payments\Tests\Gateways\Contract;
+
+use Nyholm\Psr7\Factory\Psr17Factory;
+use PHPUnit\Framework\TestCase;
+use Yiisoft\Payments\Models\Customer;
+use Yiisoft\Payments\Models\PaymentIntent;
+use Yiisoft\Payments\PaymentGatewayInterface;
+use Yiisoft\Payments\Tests\Support\TestHttpClient;
+
+abstract class GatewayContractTestCase extends TestCase
+{
+    protected TestHttpClient $http;
+    private PaymentGatewayInterface $gateway;
+
+    protected function setUp(): void
+    {
+        $factory = new Psr17Factory();
+        $this->http = new TestHttpClient($factory);
+        $this->gateway = $this->createGateway($this->http, $factory);
+    }
+
+    abstract protected function createGateway(TestHttpClient $http, Psr17Factory $factory): PaymentGatewayInterface;
+
+    abstract protected function givenCreatePaymentIntent(): PaymentIntent;
+
+    abstract protected function expectedCreatedIntent(): IntentExpectation;
+
+    abstract protected function givenRetrievePaymentIntent(): string;
+
+    abstract protected function expectedRetrievedId(): string;
+
+    abstract protected function expectedRetrievedStatus(): string;
+
+    abstract protected function givenCreateRefund(): string;
+
+    /**
+     * @return array<string, mixed>
+     */
+    abstract protected function refundParams(): array;
+
+    /**
+     * @param array<string, mixed> $refund
+     */
+    abstract protected function assertRefundShape(array $refund): void;
+
+    abstract protected function givenCreateCustomer(): Customer;
+
+    protected function customerApiIsRemote(): bool
+    {
+        return false;
+    }
+
+    protected function expectedRemoteCustomerId(): string
+    {
+        return '';
+    }
+
+    public function testCreatePaymentIntentReturnsNormalizedIntent(): void
+    {
+        $intent = $this->givenCreatePaymentIntent();
+        $expected = $this->expectedCreatedIntent();
+
+        $result = $this->gateway->createPaymentIntent($intent);
+
+        $this->assertSame($expected->id, $result->id);
+        $this->assertSame($expected->amount, $result->amount);
+        $this->assertSame($expected->currency, $result->currency);
+        $this->assertSame($expected->status, $result->status);
+    }
+
+    public function testCreatePaymentIntentNormalizesCurrencyToUpperCaseIso(): void
+    {
+        $intent = $this->givenCreatePaymentIntent();
+
+        $currency = $this->gateway->createPaymentIntent($intent)->currency;
+
+        $this->assertNotNull($currency);
+        $this->assertSame(strtoupper($currency), $currency);
+        $this->assertSame(1, preg_match('/^[A-Z]{3}$/', $currency));
+    }
+
+    public function testRetrievePaymentIntentReturnsRequestedIntent(): void
+    {
+        $intentId = $this->givenRetrievePaymentIntent();
+
+        $result = $this->gateway->retrievePaymentIntent($intentId);
+
+        $this->assertSame($this->expectedRetrievedId(), $result->id);
+        $this->assertSame($this->expectedRetrievedStatus(), $result->status);
+    }
+
+    public function testCreateRefundReturnsNonEmptyResult(): void
+    {
+        $paymentIntentId = $this->givenCreateRefund();
+
+        $refund = $this->gateway->createRefund($paymentIntentId, $this->refundParams());
+
+        $this->assertNotEmpty($refund);
+        $this->assertRefundShape($refund);
+    }
+
+    public function testCreateCustomerPreservesIdentity(): void
+    {
+        $customer = $this->givenCreateCustomer();
+
+        $result = $this->gateway->createCustomer($customer);
+
+        $this->assertSame($customer->email, $result->email);
+        $this->assertSame($customer->name, $result->name);
+    }
+
+    public function testCreateCustomerAssignsRemoteIdWhenSupported(): void
+    {
+        if (!$this->customerApiIsRemote()) {
+            $this->markTestSkipped('Provider has no remote customer API; createCustomer is a local operation.');
+        }
+
+        $customer = $this->givenCreateCustomer();
+
+        $result = $this->gateway->createCustomer($customer);
+
+        $this->assertSame($this->expectedRemoteCustomerId(), $result->id);
+    }
+}
diff --git a/tests/Gateways/Contract/IntentExpectation.php b/tests/Gateways/Contract/IntentExpectation.php
new file mode 100644
index 0000000..74cf7fa
--- /dev/null
+++ b/tests/Gateways/Contract/IntentExpectation.php
@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Payments\Tests\Gateways\Contract;
+
+final readonly class IntentExpectation
+{
+    public function __construct(
+        public string $id,
+        public int $amount,
+        public string $currency,
+        public string $status,
+    ) {
+    }
+}
diff --git a/tests/Gateways/Contract/PayPalGatewayContractTest.php b/tests/Gateways/Contract/PayPalGatewayContractTest.php
new file mode 100644
index 0000000..8f6ad7e
--- /dev/null
+++ b/tests/Gateways/Contract/PayPalGatewayContractTest.php
@@ -0,0 +1,123 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Payments\Tests\Gateways\Contract;
+
+use Nyholm\Psr7\Factory\Psr17Factory;
+use Yiisoft\Payments\Gateways\PayPalGateway;
+use Yiisoft\Payments\Models\Customer;
+use Yiisoft\Payments\Models\PaymentIntent;
+use Yiisoft\Payments\PaymentGatewayInterface;
+use Yiisoft\Payments\Tests\Support\TestHttpClient;
+
+final class PayPalGatewayContractTest extends GatewayContractTestCase
+{
+    protected function createGateway(TestHttpClient $http, Psr17Factory $factory): PaymentGatewayInterface
+    {
+        return new PayPalGateway(
+            clientId: 'test_client_id',
+            clientSecret: 'test_client_secret',
+            sandbox: true,
+            httpClient: $http,
+            requestFactory: $factory,
+            streamFactory: $factory,
+        );
+    }
+
+    protected function givenCreatePaymentIntent(): PaymentIntent
+    {
+        $this->queueAccessToken();
+        $this->http->queueJsonResponse([
+            'id' => 'ORDER-123',
+            'intent' => 'CAPTURE',
+            'status' => 'CREATED',
+            'purchase_units' => [
+                [
+                    'amount' => ['currency_code' => 'USD', 'value' => '10.00'],
+                    'custom_id' => '12345',
+                ],
+            ],
+            'links' => [
+                ['rel' => 'approve', 'href' => 'https://www.paypal.com/checkoutnow?token=ORDER-123'],
+            ],
+        ]);
+
+        return new PaymentIntent(
+            amount: 1000,
+            currency: 'USD',
+            metadata: ['order_id' => '12345'],
+            captureMethod: false,
+        );
+    }
+
+    protected function expectedCreatedIntent(): IntentExpectation
+    {
+        return new IntentExpectation('ORDER-123', 1000, 'USD', 'CREATED');
+    }
+
+    protected function givenRetrievePaymentIntent(): string
+    {
+        $this->queueAccessToken();
+        $this->http->queueJsonResponse([
+            'id' => 'ORDER-123',
+            'status' => 'COMPLETED',
+            'purchase_units' => [
+                [
+                    'amount' => ['currency_code' => 'USD', 'value' => '10.00'],
+                ],
+            ],
+        ]);
+
+        return 'ORDER-123';
+    }
+
+    protected function expectedRetrievedId(): string
+    {
+        return 'ORDER-123';
+    }
+
+    protected function expectedRetrievedStatus(): string
+    {
+        return 'COMPLETED';
+    }
+
+    protected function givenCreateRefund(): string
+    {
+        $this->queueAccessToken();
+        $this->http->queueJsonResponse([
+            'id' => 'RFD-123',
+            'status' => 'COMPLETED',
+            'amount' => ['value' => '10.00', 'currency_code' => 'USD'],
+        ]);
+
+        return 'CAPTURE-123';
+    }
+
+    protected function refundParams(): array
+    {
+        return ['amount' => 1000];
+    }
+
+    protected function assertRefundShape(array $refund): void
+    {
+        $this->assertArrayHasKey('id', $refund);
+        $this->assertSame('RFD-123', $refund['id']);
+        $this->assertSame('COMPLETED', $refund['status']);
+        $this->assertSame(['value' => '10.00', 'currency_code' => 'USD'], $refund['amount']);
+    }
+
+    protected function givenCreateCustomer(): Customer
+    {
+        return new Customer(email: 'buyer@example.com', name: 'Test Buyer');
+    }
+
+    private function queueAccessToken(): void
+    {
+        $this->http->queueJsonResponse([
+            'access_token' => 'test_access_token',
+            'expires_in' => 3600,
+            'token_type' => 'Bearer',
+        ]);
+    }
+}
diff --git a/tests/Gateways/Contract/RobokassaGatewayContractTest.php b/tests/Gateways/Contract/RobokassaGatewayContractTest.php
new file mode 100644
index 0000000..48008f7
--- /dev/null
+++ b/tests/Gateways/Contract/RobokassaGatewayContractTest.php
@@ -0,0 +1,111 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Payments\Tests\Gateways\Contract;
+
+use Nyholm\Psr7\Factory\Psr17Factory;
+use Yiisoft\Payments\Gateways\RobokassaGateway;
+use Yiisoft\Payments\Models\Customer;
+use Yiisoft\Payments\Models\PaymentIntent;
+use Yiisoft\Payments\PaymentGatewayInterface;
+use Yiisoft\Payments\Tests\Support\TestHttpClient;
+
+final class RobokassaGatewayContractTest extends GatewayContractTestCase
+{
+    protected function createGateway(TestHttpClient $http, Psr17Factory $factory): PaymentGatewayInterface
+    {
+        return new RobokassaGateway(
+            merchantLogin: 'demo',
+            password1: 'pass1',
+            password2: 'pass2',
+            password3: 'pass3',
+            testMode: true,
+            httpClient: $http,
+            requestFactory: $factory,
+            streamFactory: $factory,
+        );
+    }
+
+    protected function givenCreatePaymentIntent(): PaymentIntent
+    {
+        $this->http->queueJsonResponse([
+            'InvoiceID' => 123,
+            'InvoiceUrl' => 'https://auth.robokassa.ru/Merchant/Index.aspx?InvoiceID=123',
+            'Status' => 'CREATED',
+        ]);
+
+        return new PaymentIntent(
+            amount: 2500,
+            currency: 'RUB',
+            metadata: ['InvId' => 123, 'Description' => 'Test invoice'],
+            captureMethod: false,
+        );
+    }
+
+    protected function expectedCreatedIntent(): IntentExpectation
+    {
+        return new IntentExpectation('123', 2500, 'RUB', 'CREATED');
+    }
+
+    protected function givenRetrievePaymentIntent(): string
+    {
+        $xml = <<<XML
+        <?xml version="1.0" encoding="utf-8"?>
+        <OperationStateResponse>
+          <Result>
+            <Code>0</Code>
+            <Description>OK</Description>
+          </Result>
+          <State>
+            <Code>5</Code>
+          </State>
+          <Info>
+            <OpKey>OP-123</OpKey>
+          </Info>
+        </OperationStateResponse>
+        XML;
+
+        $this->http->queueRawResponse($xml, 200, ['Content-Type' => ['text/xml']]);
+
+        return '123';
+    }
+
+    protected function expectedRetrievedId(): string
+    {
+        return '123';
+    }
+
+    protected function expectedRetrievedStatus(): string
+    {
+        return 'SUCCEEDED';
+    }
+
+    protected function givenCreateRefund(): string
+    {
+        $this->http->queueJsonResponse([
+            'success' => true,
+            'requestId' => 'REQ-123',
+            'message' => null,
+        ]);
+
+        return '123';
+    }
+
+    protected function refundParams(): array
+    {
+        return ['amount' => 1000, 'op_key' => 'OP-123'];
+    }
+
+    protected function assertRefundShape(array $refund): void
+    {
+        $this->assertArrayHasKey('requestId', $refund);
+        $this->assertTrue($refund['success']);
+        $this->assertSame('REQ-123', $refund['requestId']);
+    }
+
+    protected function givenCreateCustomer(): Customer
+    {
+        return new Customer(email: 'buyer@example.com', name: 'Test Buyer');
+    }
+}
diff --git a/tests/Gateways/Contract/StripeGatewayContractTest.php b/tests/Gateways/Contract/StripeGatewayContractTest.php
new file mode 100644
index 0000000..4f08440
--- /dev/null
+++ b/tests/Gateways/Contract/StripeGatewayContractTest.php
@@ -0,0 +1,114 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Payments\Tests\Gateways\Contract;
+
+use Nyholm\Psr7\Factory\Psr17Factory;
+use Psr\Log\NullLogger;
+use Yiisoft\Payments\Gateways\StripeGateway;
+use Yiisoft\Payments\Models\Customer;
+use Yiisoft\Payments\Models\PaymentIntent;
+use Yiisoft\Payments\PaymentGatewayInterface;
+use Yiisoft\Payments\Tests\Support\TestHttpClient;
+
+final class StripeGatewayContractTest extends GatewayContractTestCase
+{
+    protected function createGateway(TestHttpClient $http, Psr17Factory $factory): PaymentGatewayInterface
+    {
+        return new StripeGateway('test_api_key', $http, $factory, $factory, new NullLogger());
+    }
+
+    protected function givenCreatePaymentIntent(): PaymentIntent
+    {
+        $this->http->queueJsonResponse([
+            'id' => 'pi_test123',
+            'amount' => 1000,
+            'currency' => 'usd',
+            'status' => 'requires_confirmation',
+            'client_secret' => 'pi_test123_secret',
+        ]);
+
+        return new PaymentIntent(amount: 1000, currency: 'usd');
+    }
+
+    protected function expectedCreatedIntent(): IntentExpectation
+    {
+        return new IntentExpectation('pi_test123', 1000, 'USD', 'requires_confirmation');
+    }
+
+    protected function givenRetrievePaymentIntent(): string
+    {
+        $this->http->queueJsonResponse([
+            'id' => 'pi_test123',
+            'amount' => 1000,
+            'currency' => 'usd',
+            'customer' => 'cus_test123',
+            'payment_method' => 'pm_test123',
+            'description' => 'Test payment',
+            'metadata' => [],
+            'status' => 'succeeded',
+            'created' => 1700000000,
+        ]);
+
+        return 'pi_test123';
+    }
+
+    protected function expectedRetrievedId(): string
+    {
+        return 'pi_test123';
+    }
+
+    protected function expectedRetrievedStatus(): string
+    {
+        return 'succeeded';
+    }
+
+    protected function givenCreateRefund(): string
+    {
+        $this->http->queueJsonResponse([
+            'id' => 're_test123',
+            'amount' => 1000,
+            'currency' => 'usd',
+            'status' => 'succeeded',
+            'payment_intent' => 'pi_test123',
+        ]);
+
+        return 'pi_test123';
+    }
+
+    protected function refundParams(): array
+    {
+        return ['amount' => 1000];
+    }
+
+    protected function assertRefundShape(array $refund): void
+    {
+        $this->assertArrayHasKey('id', $refund);
+        $this->assertSame('re_test123', $refund['id']);
+        $this->assertSame(1000, $refund['amount']);
+        $this->assertSame('usd', $refund['currency']);
+        $this->assertSame('succeeded', $refund['status']);
+    }
+
+    protected function givenCreateCustomer(): Customer
+    {
+        $this->http->queueJsonResponse([
+            'id' => 'cus_test123',
+            'email' => 'buyer@example.com',
+            'name' => 'Test Buyer',
+        ]);
+
+        return new Customer(email: 'buyer@example.com', name: 'Test Buyer');
+    }
+
+    protected function customerApiIsRemote(): bool
+    {
+        return true;
+    }
+
+    protected function expectedRemoteCustomerId(): string
+    {
+        return 'cus_test123';
+    }
+}
diff --git a/tests/Gateways/Contract/YooKassaGatewayContractTest.php b/tests/Gateways/Contract/YooKassaGatewayContractTest.php
new file mode 100644
index 0000000..7b26167
--- /dev/null
+++ b/tests/Gateways/Contract/YooKassaGatewayContractTest.php
@@ -0,0 +1,107 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Payments\Tests\Gateways\Contract;
+
+use Nyholm\Psr7\Factory\Psr17Factory;
+use Psr\Log\NullLogger;
+use Yiisoft\Payments\Gateways\YooKassaGateway;
+use Yiisoft\Payments\Models\Customer;
+use Yiisoft\Payments\Models\PaymentIntent;
+use Yiisoft\Payments\PaymentGatewayInterface;
+use Yiisoft\Payments\Tests\Support\TestHttpClient;
+
+final class YooKassaGatewayContractTest extends GatewayContractTestCase
+{
+    protected function createGateway(TestHttpClient $http, Psr17Factory $factory): PaymentGatewayInterface
+    {
+        return new YooKassaGateway('shop_id', 'secret_key', $http, $factory, $factory, new NullLogger());
+    }
+
+    protected function givenCreatePaymentIntent(): PaymentIntent
+    {
+        $this->http->queueJsonResponse([
+            'id' => '30ae77b9-000f-5001-8000-13e0de458932',
+            'status' => 'pending',
+            'amount' => ['value' => '100.00', 'currency' => 'RUB'],
+            'description' => 'Test payment',
+            'payment_method' => ['type' => 'bank_card', 'id' => 'pm_test123'],
+            'created_at' => '2025-11-18T12:18:01.563Z',
+            'confirmation' => [
+                'type' => 'redirect',
+                'confirmation_url' => 'https://yoomoney.ru/checkout/payments/v2/contract?orderId=30ae77b9',
+            ],
+            'metadata' => [],
+        ]);
+
+        return new PaymentIntent(
+            amount: 10000,
+            currency: 'rub',
+            paymentMethodId: 'bank_card',
+            metadata: ['return_url' => 'https://example.com/return'],
+        );
+    }
+
+    protected function expectedCreatedIntent(): IntentExpectation
+    {
+        return new IntentExpectation('30ae77b9-000f-5001-8000-13e0de458932', 10000, 'RUB', 'pending');
+    }
+
+    protected function givenRetrievePaymentIntent(): string
+    {
+        $this->http->queueJsonResponse([
+            'id' => '30ae77b9-000f-5001-8000-13e0de458932',
+            'status' => 'succeeded',
+            'amount' => ['value' => '100.00', 'currency' => 'RUB'],
+            'description' => 'Test payment',
+            'payment_method' => ['type' => 'bank_card', 'id' => 'pm_test123'],
+            'created_at' => '2025-11-19T03:44:43.200Z',
+        ]);
+
+        return '30ae77b9-000f-5001-8000-13e0de458932';
+    }
+
+    protected function expectedRetrievedId(): string
+    {
+        return '30ae77b9-000f-5001-8000-13e0de458932';
+    }
+
+    protected function expectedRetrievedStatus(): string
+    {
+        return 'succeeded';
+    }
+
+    protected function givenCreateRefund(): string
+    {
+        $this->http->queueJsonResponse([
+            'id' => '30af6093-0015-5001-8000-196e1cbaceef',
+            'payment_id' => '30af50eb-000f-5001-8000-1533ca71a452',
+            'status' => 'succeeded',
+            'created_at' => '2025-11-19T04:51:31.067Z',
+            'amount' => ['value' => '100.00', 'currency' => 'RUB'],
+        ]);
+
+        return '30af50eb-000f-5001-8000-1533ca71a452';
+    }
+
+    protected function refundParams(): array
+    {
+        return ['amount' => 10000, 'currency' => 'rub'];
+    }
+
+    protected function assertRefundShape(array $refund): void
+    {
+        $this->assertArrayHasKey('id', $refund);
+        $this->assertSame('30af6093-0015-5001-8000-196e1cbaceef', $refund['id']);
+        $this->assertSame('30af50eb-000f-5001-8000-1533ca71a452', $refund['payment_id']);
+        $this->assertSame(10000, $refund['amount']);
+        $this->assertSame('rub', $refund['currency']);
+        $this->assertSame('succeeded', $refund['status']);
+    }
+
+    protected function givenCreateCustomer(): Customer
+    {
+        return new Customer(email: 'buyer@example.com', name: 'Test Buyer');
+    }
+}