diff --git a/README.md b/README.md
index 3811bea..00cfb4a 100644
--- a/README.md
+++ b/README.md
@@ -1,73 +1,85 @@
-Google Pub/Sub transport implementation for Symfony Messenger
-========
-
-This bundle provides a simple implementation of Google Pub/Sub transport for Symfony Messenger.
-
-The bundle requires only `symfony/messenger`, `google/cloud-pubsub` and `symfony/options-resolver` packages. 
-In contrast with [Enqueue GPS transport](https://github.com/php-enqueue/gps),
-it doesn't require [Enqueue](https://github.com/php-enqueue) 
-and [some bridge](https://github.com/sroze/messenger-enqueue-transport#readme). 
-It supports ordering messages with `OrderingKeyStamp` and it's not outdated. 
-
-## Installation
-
-### Step 1: Install the Bundle
-
-From within container execute the following command to download the latest version of the bundle:
-
-```console
-$ composer require petitpress/gps-messenger-bundle --no-scripts
-```
-
-### Step 2: Configure environment variables
-
-Official [Google Cloud PubSub SDK](https://github.com/googleapis/google-cloud-php-pubsub) 
-requires some globally accessible environment variables.
-
-You might need to change default Symfony DotEnv instance to use `putenv` 
-as Google needs to access some variables through `getenv`. To do so, use putenv method in `config/bootstrap.php`:
-```php
-(new Dotenv())->usePutenv()->...
-```
-
-List of Google Pub/Sub configurable variables :
-```dotenv
-# use these for production environemnt:
-GOOGLE_APPLICATION_CREDENTIALS='google-pubsub-credentials.json'
-GCLOUD_PROJECT='project-id'
-
-# use these for development environemnt (if you have installed Pub/Sub emulator):
-PUBSUB_EMULATOR_HOST=http://localhost:8538
-```
-
-### Step 3: Configure Symfony Messenger
-```yaml
-# config/packages/messenger.yaml
-
-framework:
-    messenger:
-        transports:
-            gps_transport:
-                dsn: 'gps://default'
-                options:
-                    max_messages_pull: 10 # optional (default: 10)
-                    topic: # optional (default name: messages)
-                        name: 'messages'
-                    queue: # optional (default the same as topic.name)
-                        name: 'messages'
-```
-or:
-```yaml
-# config/packages/messenger.yaml
-
-framework:
-    messenger:
-        transports:
-            gps_transport:
-                dsn: 'gps://default/messages?max_messages_pull=10'
-```
-
-### Step 4: Use available stamps if needed
-
-* `OrderingKeyStamp`: use for keeping messages of the same context in order. 
-  For more information, read an [official documentation](https://cloud.google.com/pubsub/docs/publisher#using_ordering_keys). 
\ No newline at end of file
+Google Pub/Sub transport implementation for Symfony Messenger
+========
+
+This bundle provides a simple implementation of Google Pub/Sub transport for Symfony Messenger.
+
+The bundle requires only `symfony/messenger`, `google/cloud-pubsub` and `symfony/options-resolver` packages. 
+In contrast with [Enqueue GPS transport](https://github.com/php-enqueue/gps),
+it doesn't require [Enqueue](https://github.com/php-enqueue) 
+and [some bridge](https://github.com/sroze/messenger-enqueue-transport#readme). 
+It supports ordering messages with `OrderingKeyStamp` and it's not outdated. 
+
+## Installation
+
+### Step 1: Install the Bundle
+
+From within container execute the following command to download the latest version of the bundle:
+
+```console
+$ composer require petitpress/gps-messenger-bundle --no-scripts
+```
+
+### Step 2: Configure environment variables
+
+Official [Google Cloud PubSub SDK](https://github.com/googleapis/google-cloud-php-pubsub) 
+requires some globally accessible environment variables.
+
+If you want to provide the PubSub authentication info through environment variables
+you might need to change default Symfony DotEnv instance to use `putenv` 
+as Google needs to access some variables through `getenv`. To do so, use putenv method in `config/bootstrap.php` 
+(does no longer exist in Symfony 5.3 and above):
+```php
+(new Dotenv())->usePutenv()->...
+```
+
+List of Google Pub/Sub configurable variables :
+```dotenv
+# use these for production environemnt:
+GOOGLE_APPLICATION_CREDENTIALS='google-pubsub-credentials.json'
+GOOGLE_CLOUD_PROJECT='project-id'
+
+# use these for development environemnt (if you have installed Pub/Sub emulator):
+PUBSUB_EMULATOR_HOST=http://localhost:8538
+```
+
+If you want to use the bundle with Symfony Version 5.3 and above you need to configure those variables 
+inside the `config/packages/messenger.yaml`.
+
+### Step 3: Configure Symfony Messenger
+```yaml
+# config/packages/messenger.yaml
+
+framework:
+    messenger:
+        transports:
+            gps_transport:
+                dsn: 'gps://default'
+                options:
+                    max_messages_pull: 10 # optional (default: 10)
+                    topic: # optional (default name: messages)
+                        name: 'messages'
+                    queue: # optional (default the same as topic.name)
+                        name: 'messages'
+                        
+                    # optional (see google-cloud-php-pubsub documentation on GOOGLE_APPLICATION_CREDENTIALS)
+                    keyFilePath: '%env(GOOGLE_APPLICATION_CREDENTIALS)%'
+                    # optional (see google-cloud-php-pubsub documentation on PUBSUB_EMULATOR_HOST)
+                    emulatorHost: '%env(PUBSUB_EMULATOR_HOST)%'
+                    # mandatory (see google-cloud-php-pubsub documentation on GOOGLE_CLOUD_PROJECT)
+                    projectId: '%env(GOOGLE_CLOUD_PROJECT)%'
+```
+or:
+```yaml
+# config/packages/messenger.yaml
+
+framework:
+    messenger:
+        transports:
+            gps_transport:
+                dsn: 'gps://default/messages?max_messages_pull=10'
+```
+
+### Step 4: Use available stamps if needed
+
+* `OrderingKeyStamp`: use for keeping messages of the same context in order. 
+  For more information, read an [official documentation](https://cloud.google.com/pubsub/docs/publisher#using_ordering_keys). 
diff --git a/Tests/Resources/credentials.json b/Tests/Resources/credentials.json
new file mode 100644
index 0000000..0967ef4
--- /dev/null
+++ b/Tests/Resources/credentials.json
@@ -0,0 +1 @@
+{}
diff --git a/Tests/Transport/GpsTransportFactoryTest.php b/Tests/Transport/GpsTransportFactoryTest.php
new file mode 100644
index 0000000..4fe0e93
--- /dev/null
+++ b/Tests/Transport/GpsTransportFactoryTest.php
@@ -0,0 +1,94 @@
+<?php
+
+namespace Transport;
+
+use Google\Cloud\Core\Exception\GoogleException;
+use PetitPress\GpsMessengerBundle\Transport\GpsConfigurationInterface;
+use PetitPress\GpsMessengerBundle\Transport\GpsConfigurationResolverInterface;
+use PetitPress\GpsMessengerBundle\Transport\GpsTransport;
+use PetitPress\GpsMessengerBundle\Transport\GpsTransportFactory;
+use PHPUnit\Framework\TestCase;
+use Prophecy\Argument;
+use Prophecy\PhpUnit\ProphecyTrait;
+use Prophecy\Prophecy\ObjectProphecy;
+use Symfony\Component\Messenger\Transport\Serialization\SerializerInterface;
+
+class GpsTransportFactoryTest extends TestCase
+{
+    use ProphecyTrait;
+
+    private ObjectProphecy $serializerProphecy;
+    private GpsTransportFactory $gpsTransportFactory;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $gpsConfigurtionProphecy = $this->prophesize(GpsConfigurationInterface::class);
+        $gpsCongigurationResolverProphecy = $this->prophesize(GpsConfigurationResolverInterface::class);
+        $this->serializerProphecy = $this->prophesize(SerializerInterface::class);
+
+        $gpsCongigurationResolverProphecy->resolve(Argument::any(), Argument::any())->willReturn($gpsConfigurtionProphecy->reveal());
+
+        $this->gpsTransportFactory = new GpsTransportFactory($gpsCongigurationResolverProphecy->reveal());
+    }
+
+    public function testCreateTransportFailsWithoutProjectId()
+    {
+        $dsn = 'gps://';
+        $options = [];
+
+        static::assertFalse(getenv(GpsTransportFactory::GOOGLE_CLOUD_PROJECT));
+
+        $this->expectException(GoogleException::class);
+
+        $this->gpsTransportFactory->createTransport($dsn, $options, $this->serializerProphecy->reveal());
+    }
+
+    public function testCreateTransportWithProjectIdFromEnvironmentVar()
+    {
+        $dsn = 'gps://';
+        $options = [];
+
+        putenv(GpsTransportFactory::GOOGLE_CLOUD_PROJECT . '=' . 'random');
+
+        $transport = $this->gpsTransportFactory->createTransport($dsn, $options, $this->serializerProphecy->reveal());
+
+        static::assertInstanceOf(GpsTransport::class, $transport);
+        static::assertEquals('random', getenv(GpsTransportFactory::GOOGLE_CLOUD_PROJECT));
+        static::assertFalse(getenv(GpsTransportFactory::GOOGLE_APPLICATION_CREDENTIALS));
+        static::assertFalse(getenv(GpsTransportFactory::PUBSUB_EMULATOR_HOST));
+    }
+
+    public function testCreateTransportWithProjectIdFromEnvironmentVarAndConfiguration()
+    {
+        $dsn = 'gps://';
+        $options = ['projectId' => 'specfic'];
+
+        putenv(GpsTransportFactory::GOOGLE_CLOUD_PROJECT . '=' . 'random');
+
+        $transport = $this->gpsTransportFactory->createTransport($dsn, $options, $this->serializerProphecy->reveal());
+
+        static::assertInstanceOf(GpsTransport::class, $transport);
+        static::assertEquals('specfic', getenv(GpsTransportFactory::GOOGLE_CLOUD_PROJECT));
+        static::assertFalse(getenv(GpsTransportFactory::GOOGLE_APPLICATION_CREDENTIALS));
+        static::assertFalse(getenv(GpsTransportFactory::PUBSUB_EMULATOR_HOST));
+    }
+
+    public function testCreateTransportWithEmulator()
+    {
+        $dsn = 'gps://';
+        $options = [
+            'projectId' => 'random',
+            'emulatorHost' => 'address://emulator/host',
+            'keyFilePath' => __DIR__ . '/../Resources/credentials.json'
+        ];
+
+        $transport = $this->gpsTransportFactory->createTransport($dsn, $options, $this->serializerProphecy->reveal());
+
+        static::assertInstanceOf(GpsTransport::class, $transport);
+        static::assertEquals(__DIR__ . '/../Resources/credentials.json', getenv(GpsTransportFactory::GOOGLE_APPLICATION_CREDENTIALS));
+        static::assertEquals('random', getenv(GpsTransportFactory::GOOGLE_CLOUD_PROJECT));
+        static::assertEquals('address://emulator/host', getenv(GpsTransportFactory::PUBSUB_EMULATOR_HOST));
+    }
+}
diff --git a/Transport/GpsTransportFactory.php b/Transport/GpsTransportFactory.php
index 55b4580..74d5985 100644
--- a/Transport/GpsTransportFactory.php
+++ b/Transport/GpsTransportFactory.php
@@ -1,43 +1,67 @@
-<?php
-
-declare(strict_types=1);
-
-namespace PetitPress\GpsMessengerBundle\Transport;
-
+<?php
+
+declare(strict_types=1);
+
+namespace PetitPress\GpsMessengerBundle\Transport;
+
 use Google\Cloud\PubSub\PubSubClient;
 use Symfony\Component\Messenger\Transport\Serialization\SerializerInterface;
 use Symfony\Component\Messenger\Transport\TransportFactoryInterface;
-use Symfony\Component\Messenger\Transport\TransportInterface;
-
+use Symfony\Component\Messenger\Transport\TransportInterface;
+
 /**
  * @author Ronald Marfoldi <ronald.marfoldi@petitpress.sk>
- */
+ */
 final class GpsTransportFactory implements TransportFactoryInterface
 {
-    private GpsConfigurationResolverInterface $gpsConfigurationResolver;
-
+    const GOOGLE_APPLICATION_CREDENTIALS = 'GOOGLE_APPLICATION_CREDENTIALS';
+    const GOOGLE_CLOUD_PROJECT = 'GOOGLE_CLOUD_PROJECT';
+    const PUBSUB_EMULATOR_HOST = 'PUBSUB_EMULATOR_HOST';
+
+    private GpsConfigurationResolverInterface $gpsConfigurationResolver;
+
     public function __construct(GpsConfigurationResolverInterface $gpsConfigurationResolver)
     {
         $this->gpsConfigurationResolver = $gpsConfigurationResolver;
-    }
-
+    }
+
     /**
      * {@inheritdoc}
-     */
+     */
     public function createTransport(string $dsn, array $options, SerializerInterface $serializer): TransportInterface
     {
+        $this->resolvePubSubEnvOptions($options);
+
         return new GpsTransport(
-            new PubSubClient(),
-            $this->gpsConfigurationResolver->resolve($dsn, $options),
+            new PubSubClient(),
+            $this->gpsConfigurationResolver->resolve($dsn, $options),
             $serializer
         );
-    }
-
+    }
+
+    protected function resolvePubSubEnvOptions(array &$options): void
+    {
+        $envMap = [
+            'projectId' => self::GOOGLE_CLOUD_PROJECT,
+            'emulatorHost' => self::PUBSUB_EMULATOR_HOST,
+            'keyFilePath' => self::GOOGLE_APPLICATION_CREDENTIALS
+        ];
+
+        foreach ($envMap as $optKey => $envKey) {
+            if (array_key_exists($optKey, $options)) {
+                if (!empty($options[$optKey])) {
+                    putenv($envKey . '=' . $options[$optKey]);
+                }
+                unset($options[$optKey]);
+            }
+        }
+    }
+
     /**
      * {@inheritdoc}
-     */
+     */
     public function supports(string $dsn, array $options): bool
     {
         return str_starts_with($dsn, 'gps://');
     }
-}
\ No newline at end of file
+}