diff --git a/DEVELOPPING.md b/DEVELOPPING.md
index 6406815..08edd2a 100644
--- a/DEVELOPPING.md
+++ b/DEVELOPPING.md
@@ -120,4 +120,4 @@ Maintaining code quality by adding the custom post-commit hook to yours.
 
 ```bash
 cat ./scripts/hooks/post-commit >> ./.git/hooks/post-commit
-```
\ No newline at end of file
+```
diff --git a/commerce_google_tag_manager.info.yml b/commerce_google_tag_manager.info.yml
index 5f62e79..ce11218 100644
--- a/commerce_google_tag_manager.info.yml
+++ b/commerce_google_tag_manager.info.yml
@@ -6,4 +6,4 @@ type: module
 dependencies:
 - drupal:google_tag
 - drupal:commerce
-- drupal:commerce_checkout
\ No newline at end of file
+- drupal:commerce_checkout
diff --git a/tests/src/Kernel/AlterProductEventTest.php b/tests/src/Kernel/AlterProductEventTest.php
new file mode 100644
index 0000000..33c3257
--- /dev/null
+++ b/tests/src/Kernel/AlterProductEventTest.php
@@ -0,0 +1,70 @@
+<?php
+
+namespace Drupal\Tests\commerce_google_tag_manager\Kernel;
+
+use Drupal\commerce_google_tag_manager\Event\AlterProductEvent;
+use Drupal\commerce_product\Entity\ProductVariationInterface;
+use Drupal\commerce_product\Entity\ProductVariation;
+use Drupal\commerce_google_tag_manager\Product;
+
+/**
+ * @coversDefaultClass \Drupal\commerce_google_tag_manager\Event\AlterProductEvent
+ *
+ * @group commerce
+ * @group commerce_google_tag_manager
+ * @group commerce_google_tag_manager_kernel
+ */
+class AlterProductEventTest extends CommerceKernelTestBase {
+  /**
+   * The variations to test with.
+   *
+   * @var \Drupal\commerce_product\Entity\ProductVariationInterface
+   */
+  protected $variation;
+
+  /**
+   * The GTM product to test against.
+   *
+   * @var \Drupal\commerce_google_tag_manager\Product
+   */
+  protected $product;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    // The variations to test with.
+    $this->variation = ProductVariation::create([
+      'type'   => 'default',
+      'sku'    => $this->randomString(10),
+      'status' => TRUE,
+    ]);
+    $this->variation->save();
+
+    $this->product = new Product();
+    $this->product
+      ->setName($this->randomString(16))
+      ->setId(1)
+      ->setVariant($this->variation->getTitle())
+      ->setPrice('11.99');
+  }
+
+  /**
+   * @covers ::getProduct
+   */
+  public function testGetProduct() {
+    $event = new AlterProductEvent($this->product, $this->variation);
+    $this->assertInstanceOf(Product::class, $event->getProduct());
+  }
+
+  /**
+   * @covers ::getProductVariation
+   */
+  public function testGetProductVariation() {
+    $event = new AlterProductEvent($this->product, $this->variation);
+    $this->assertInstanceOf(ProductVariationInterface::class, $event->getProductVariation());
+  }
+
+}
diff --git a/tests/src/Kernel/CommerceKernelTestBase.php b/tests/src/Kernel/CommerceKernelTestBase.php
new file mode 100644
index 0000000..4c502ce
--- /dev/null
+++ b/tests/src/Kernel/CommerceKernelTestBase.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Drupal\Tests\commerce_google_tag_manager\Kernel;
+
+use Drupal\Tests\commerce\Kernel\CommerceKernelTestBase as DrupalCommerceKernelTestBase;
+
+/**
+ * Provides a base class for Commerce Google Tag Manager kernel tests.
+ */
+abstract class CommerceKernelTestBase extends DrupalCommerceKernelTestBase {
+
+  /**
+   * Modules to additionnaly enable.
+   *
+   * @var array
+   */
+  public static $modules = [
+    'commerce_product',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installEntitySchema('commerce_product_variation');
+    $this->installEntitySchema('commerce_product');
+    $this->installConfig(['commerce_product']);
+  }
+
+}
diff --git a/tests/src/Kernel/EventStorageServiceTest.php b/tests/src/Kernel/EventStorageServiceTest.php
new file mode 100644
index 0000000..26769d5
--- /dev/null
+++ b/tests/src/Kernel/EventStorageServiceTest.php
@@ -0,0 +1,182 @@
+<?php
+
+namespace Drupal\Tests\commerce_google_tag_manager\Kernel;
+
+use Drupal\Tests\commerce\Kernel\CommerceKernelTestBase;
+use Drupal\commerce_google_tag_manager\EventTrackerService;
+
+/**
+ * @coversDefaultClass \Drupal\commerce_google_tag_manager\EventStorageService
+ *
+ * @group commerce
+ * @group commerce_google_tag_manager
+ * @group commerce_google_tag_manager_kernel
+ */
+class EventStorageServiceTest extends CommerceKernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = [
+    'commerce_checkout',
+    'commerce_google_tag_manager',
+  ];
+
+  /**
+   * The tempstore object.
+   *
+   * @var \Drupal\Core\TempStore\PrivateTempStore
+   */
+  private $tempStore;
+
+  /**
+   * The Commerce GTM event storage.
+   *
+   * @var \Drupal\commerce_google_tag_manager\EventStorageService
+   */
+  private $eventStorage;
+
+  /**
+   * The Google Tag Manager Product Detail view event structure to test with.
+   *
+   * @var array
+   */
+  protected $detailEvent;
+
+  /**
+   * The Google Tag Manager Checkout event structure to test with.
+   *
+   * @var array
+   */
+  protected $checkoutEvent;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installSchema('system', ['key_value_expire']);
+
+    $this->tempStore = $this->container->get('tempstore.private')->get('commerce_google_tag_manager');
+    $this->eventStorage = $this->container->get('commerce_google_tag_manager.event_storage');
+
+    $this->detailEvent = [
+      'event' => EventTrackerService::EVENT_PRODUCT_DETAIL_VIEWS,
+      'ecommerce' => [
+        'detail' => [
+          'actionField' => [
+            'list' => '',
+          ],
+          'products' => [
+            0 => [
+              'name'    => 'Lorem Ipsum',
+              'id'      => '1',
+              'price'   => '11.99',
+              'variant' => 'Lorem Ipsum',
+            ],
+          ],
+        ],
+      ],
+    ];
+
+    $this->checkoutEvent = [
+      'event' => EventTrackerService::EVENT_CHECKOUT,
+      'ecommerce' => [
+        'checkout' => [
+          'actionField' => [
+            'step' => 1,
+          ],
+          'products' => [
+            0 => [
+              'name'    => 'Lorem Ipsum',
+              'id'      => '1',
+              'price'   => '11.99',
+              'variant' => 'Lorem Ipsum',
+              'quantity' => 1,
+            ],
+          ],
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * @covers ::getEvents
+   */
+  public function testGetEvents() {
+    $this->tempStore->set('events', [
+      '0e05cdf318b5832a7caf62ad11d386f4' => $this->detailEvent,
+    ]);
+    $result = $this->eventStorage->getEvents();
+    $this->assertSame([0 => $this->detailEvent], $result);
+  }
+
+  /**
+   * @covers ::getEvents
+   */
+  public function testGetEventsEmpty() {
+    $this->tempStore->set('events', NULL);
+    $result = $this->eventStorage->getEvents();
+    $this->assertInternalType('array', $result);
+    $this->assertEmpty($result);
+  }
+
+  /**
+   * @covers ::flush
+   */
+  public function testFlush() {
+    $this->tempStore->set('events', [
+      '0e05cdf318b5832a7caf62ad11d386f4' => $this->detailEvent,
+    ]);
+    $this->eventStorage->flush();
+    $result = $this->tempStore->get('events');
+    $this->assertNull($result);
+  }
+
+  /**
+   * @covers ::addEvent
+   *
+   * Asserts usage of Private Temp Store for events queue.
+   */
+  public function testAddEvent() {
+    $this->eventStorage->addEvent($this->detailEvent);
+
+    $result = $this->tempStore->get('events');
+    $this->assertInternalType('array', $result);
+    $this->assertSame([
+      '0e05cdf318b5832a7caf62ad11d386f4' => $this->detailEvent,
+    ], $result);
+  }
+
+  /**
+   * @covers ::addEvent
+   *
+   * Asserts the events queue follows the FIFO (First in First out) pattern.
+   */
+  public function testAddEventFifoQueue() {
+    $this->eventStorage->addEvent($this->detailEvent);
+    $this->eventStorage->addEvent($this->checkoutEvent);
+    $events = $this->tempStore->get('events');
+
+    $this->assertSame([
+      '0e05cdf318b5832a7caf62ad11d386f4' => $this->detailEvent,
+      '5d92a6ab1f5bd49c7ac5a065302dcb16' => $this->checkoutEvent,
+    ], $events);
+  }
+
+  /**
+   * @covers ::addEvent
+   *
+   * Asserts strictly same event aren't added twice in the events queue.
+   */
+  public function testAddEventSameSkipped() {
+    $this->eventStorage->addEvent($this->detailEvent);
+    $this->eventStorage->addEvent($this->detailEvent);
+    $events = $this->tempStore->get('events');
+    $this->assertSame([
+      '0e05cdf318b5832a7caf62ad11d386f4' => $this->detailEvent,
+    ], $events);
+  }
+
+}
diff --git a/tests/src/Unit/AlterEventDataEventTest.php b/tests/src/Unit/AlterEventDataEventTest.php
new file mode 100644
index 0000000..71accdd
--- /dev/null
+++ b/tests/src/Unit/AlterEventDataEventTest.php
@@ -0,0 +1,184 @@
+<?php
+
+namespace Drupal\Tests\commerce_google_tag_manager\Unit;
+
+use Drupal\Tests\UnitTestCase;
+use Drupal\commerce_google_tag_manager\Event\AlterEventDataEvent;
+use Drupal\commerce_google_tag_manager\EventTrackerService;
+
+/**
+ * @coversDefaultClass \Drupal\commerce_google_tag_manager\Event\AlterEventDataEvent
+ *
+ * @group commerce
+ * @group commerce_google_tag_manager
+ * @group commerce_google_tag_manager_unit
+ */
+class AlterEventDataEventTest extends UnitTestCase {
+
+  /**
+   * The event to tests against.
+   *
+   * @var \Drupal\commerce_google_tag_manager\Event\AlterEventDataEvent
+   */
+  protected $alterEventData;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+    $this->alterEventData = new AlterEventDataEvent([]);
+  }
+
+  /**
+   * @covers ::setEventData
+   * @covers ::getEventData
+   *
+   * @dataProvider eventData
+   */
+  public function testSetEventDetailViews($event_data) {
+    $this->alterEventData->setEventData($event_data);
+    $this->assertSame($event_data, $this->alterEventData->getEventData());
+  }
+
+  /**
+   * List of supported event data.
+   *
+   * @return array
+   *   Examples of event data structure by event types.
+   */
+  public function eventData() {
+    return [
+      'Product detail views' => [
+        [
+          'event' => EventTrackerService::EVENT_PRODUCT_DETAIL_VIEWS,
+          'ecommerce' => [
+            'detail' => [
+              'actionField' => [
+                'list' => '',
+              ],
+              'products' => [
+                0 => [
+                  'name'    => 'Lorem Ipsum',
+                  'id'      => '1',
+                  'price'   => '11.99',
+                  'variant' => 'Lorem Ipsum',
+                ],
+              ],
+            ],
+          ],
+        ],
+      ],
+
+      // @todo add product impression example.
+      'Product impressions' => [
+        [
+          'event' => EventTrackerService::EVENT_PRODUCT_IMPRESSIONS,
+          'ecommerce' => [],
+        ],
+      ],
+
+      // @todo add product click example.
+      'Product click' => [
+        [
+          'event' => EventTrackerService::EVENT_PRODUCT_CLICK,
+          'ecommerce' => [],
+        ],
+      ],
+
+      'Add to cart' => [
+        [
+          'event' => EventTrackerService::EVENT_ADD_CART,
+          'ecommerce' => [
+            'currencyCode' => 'CHF',
+            'add' => [
+              'products' => [
+                0 => [
+                  'name'    => 'Lorem Ipsum',
+                  'id'      => '1',
+                  'price'   => '11.99',
+                  'variant' => 'Lorem Ipsum',
+                  'quantity' => 1,
+                ],
+              ],
+            ],
+          ],
+        ],
+      ],
+
+      'Remove to cart' => [
+        [
+          'event' => EventTrackerService::EVENT_REMOVE_CART,
+          'ecommerce' => [
+            'remove' => [
+              'products' => [
+                0 => [
+                  'name'    => 'Lorem Ipsum',
+                  'id'      => '1',
+                  'price'   => '11.99',
+                  'variant' => 'Lorem Ipsum',
+                  'quantity' => 1,
+                ],
+              ],
+            ],
+          ],
+        ],
+      ],
+
+      'Checkout' => [
+        [
+          'event' => EventTrackerService::EVENT_CHECKOUT,
+          'ecommerce' => [
+            'checkout' => [
+              'actionField' => [
+                'step' => 1,
+              ],
+              'products' => [
+                0 => [
+                  'name'    => 'Lorem Ipsum',
+                  'id'      => '1',
+                  'price'   => '11.99',
+                  'variant' => 'Lorem Ipsum',
+                  'quantity' => 1,
+                ],
+              ],
+            ],
+          ],
+        ],
+      ],
+
+      // @todo add checkout option example.
+      'Checkout option' => [
+        [
+          'event' => EventTrackerService::EVENT_CHECKOUT_OPTION,
+          'ecommerce' => [],
+        ],
+      ],
+
+      'Purchase' => [
+        [
+          'event' => EventTrackerService::EVENT_PURCHASE,
+          'ecommerce' => [
+            'purchase' => [
+              'actionField' => [
+                'id' => '1',
+                'affiliation' => 'Commerce Website',
+                'revenue' => '11.99',
+              ],
+              'products' => [
+                0 => [
+                  'name'    => 'Lorem Ipsum',
+                  'id'      => '1',
+                  'price'   => '11.99',
+                  'variant' => 'Lorem Ipsum',
+                  'quantity' => 1,
+                ],
+              ],
+            ],
+          ],
+        ],
+      ],
+    ];
+  }
+
+}
diff --git a/tests/src/Unit/EnhancedEcommerceEventsTest.php b/tests/src/Unit/EnhancedEcommerceEventsTest.php
new file mode 100644
index 0000000..02b686d
--- /dev/null
+++ b/tests/src/Unit/EnhancedEcommerceEventsTest.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace Drupal\Tests\commerce_google_tag_manager\Unit;
+
+use Drupal\Tests\UnitTestCase;
+use Drupal\commerce_google_tag_manager\Event\EnhancedEcommerceEvents;
+
+/**
+ * @coversDefaultClass \Drupal\commerce_google_tag_manager\Event\EnhancedEcommerceEvents
+ *
+ * @group commerce
+ * @group commerce_google_tag_manager
+ * @group commerce_google_tag_manager_unit
+ */
+class EnhancedEcommerceEventsTest extends UnitTestCase {
+
+  /**
+   * @covers \Drupal\commerce_google_tag_manager\Event\EnhancedEcommerceEvents
+   *
+   * @dataProvider eventNames
+   */
+  public function testEventNames($event_name, $expected) {
+    $this->assertEquals($expected, $event_name);
+  }
+
+  /**
+   * List of supported event with expected names.
+   *
+   * @return array
+   *   The list of CONST names & string expected value.
+   */
+  public function eventNames() {
+    return [
+      [
+        EnhancedEcommerceEvents::ALTER_PRODUCT,
+        'commerce_google_tag_manager.alter_product',
+      ],
+      [
+        EnhancedEcommerceEvents::ALTER_EVENT_DATA,
+        'commerce_google_tag_manager.alter_event_data',
+      ],
+      [
+        EnhancedEcommerceEvents::TRACK_CHECKOUT_STEP,
+        'commerce_google_tag_manager.track_checkout_step',
+      ],
+    ];
+  }
+
+}
diff --git a/tests/src/Unit/EventStorageServiceTest.php b/tests/src/Unit/EventStorageServiceTest.php
new file mode 100644
index 0000000..6eb2a03
--- /dev/null
+++ b/tests/src/Unit/EventStorageServiceTest.php
@@ -0,0 +1,163 @@
+<?php
+
+namespace Drupal\Tests\commerce_google_tag_manager\Unit;
+
+use Drupal\Tests\UnitTestCase;
+use Drupal\commerce_google_tag_manager\EventStorageService;
+use Drupal\Tests\commerce_google_tag_manager\Traits\InvokeMethodTrait;
+use Drupal\commerce_google_tag_manager\EventTrackerService;
+use Drupal\Core\TempStore\PrivateTempStoreFactory;
+use Drupal\Core\TempStore\PrivateTempStore;
+use Symfony\Component\EventDispatcher\EventDispatcherInterface;
+use Drupal\commerce_google_tag_manager\Event\EnhancedEcommerceEvents;
+use Drupal\commerce_google_tag_manager\Event\AlterEventDataEvent;
+
+/**
+ * @coversDefaultClass \Drupal\commerce_google_tag_manager\EventStorageService
+ *
+ * @group commerce
+ * @group commerce_google_tag_manager
+ * @group commerce_google_tag_manager_unit
+ */
+class EventStorageServiceTest extends UnitTestCase {
+  use InvokeMethodTrait;
+
+  /**
+   * The Commerce GTM event storage.
+   *
+   * @var \Drupal\commerce_google_tag_manager\EventStorageService
+   */
+  private $eventStorage;
+
+  /**
+   * The event dispatcher.
+   *
+   * @var \Symfony\Component\EventDispatcher\EventDispatcherInterface
+   */
+  private $eventDispatcher;
+
+  /**
+   * The tempstore object.
+   *
+   * @var \Drupal\Core\TempStore\PrivateTempStore
+   */
+  private $tempStore;
+
+  /**
+   * Event to alter Enhanced Ecommerce event data.
+   *
+   * @var \Drupal\commerce_google_tag_manager\Event\AlterEventDataEvent
+   */
+  private $alterEventDataEvent;
+
+  /**
+   * The Google Tag Manager event structure to test with.
+   *
+   * @var array
+   */
+  protected $event;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+
+    $this->tempStore       = $this->getMockBuilder(PrivateTempStoreFactory::class)
+      ->disableOriginalConstructor()->getMock();
+    $this->eventDispatcher = $this->getMockBuilder(EventDispatcherInterface::class)
+      ->disableOriginalConstructor()->getMock();
+
+    $this->eventStorage = new EventStorageService($this->tempStore, $this->eventDispatcher);
+
+    $this->event = [
+      'event' => EventTrackerService::EVENT_PRODUCT_DETAIL_VIEWS,
+      'ecommerce' => [
+        'detail' => [
+          'actionField' => [
+            'list' => '',
+          ],
+          'products' => [
+            0 => [
+              'name'    => 'Lorem Ipsum',
+              'id'      => '1',
+              'price'   => '11.99',
+              'variant' => 'Lorem Ipsum',
+            ],
+          ],
+        ],
+      ],
+    ];
+    $this->alterEventDataEvent = new AlterEventDataEvent($this->event);
+  }
+
+  /**
+   * @covers ::hash
+   */
+  public function testHash() {
+    $result = $this->invokeMethod($this->eventStorage, 'hash', [$this->event]);
+    $this->assertEquals('0e05cdf318b5832a7caf62ad11d386f4', $result);
+  }
+
+  /**
+   * When addEvent called on a new event, we should fire an Event Alter.
+   *
+   * This should occure only when the added event has not already been added.
+   * This will then dispatch EnhancedEcommerceEvents::ALTER_EVENT_DATA.
+   *
+   * @covers ::addEvent
+   */
+  public function testAddEventDispatchAlter() {
+    // Mock stored events, make sure the event has never been added.
+    $stored_events = $this->getMockBuilder(PrivateTempStore::class)
+      ->disableOriginalConstructor()->getMock();
+    $stored_events->expects($this->once())
+      ->method('get')
+      ->with('events')
+      ->willReturn([]);
+
+    // Re-Mock the Private Temp Store & The Symfony Event Dispatcher.
+    $this->tempStore->expects($this->once())
+      ->method('get')
+      ->with('commerce_google_tag_manager')
+      ->willReturn($stored_events);
+    $this->eventDispatcher->expects($this->once())
+      ->method('dispatch')
+      ->with(EnhancedEcommerceEvents::ALTER_EVENT_DATA, $this->alterEventDataEvent);
+
+    $this->eventStorage = new EventStorageService($this->tempStore, $this->eventDispatcher);
+
+    $this->eventStorage->addEvent($this->event);
+  }
+
+  /**
+   * When addEvent called on a un-new event, we should not fire an Event Alter.
+   *
+   * This should occure only when the added event has already been added.
+   * This will then not dispatch EnhancedEcommerceEvents::ALTER_EVENT_DATA.
+   *
+   * @covers ::addEvent
+   */
+  public function testAddEventShouldDispatchAlterOnlyOnce() {
+    // Mock stored events, make sure the event has already been added.
+    $stored_events = $this->getMockBuilder(PrivateTempStore::class)
+      ->disableOriginalConstructor()->getMock();
+    $stored_events->expects($this->once())
+      ->method('get')
+      ->with('events')
+      ->willReturn(['0e05cdf318b5832a7caf62ad11d386f4' => $this->event]);
+
+    // Re-Mock the Private Temp Store & The Symfony Event Dispatcher.
+    $this->tempStore->expects($this->once())
+      ->method('get')
+      ->with('commerce_google_tag_manager')
+      ->willReturn($stored_events);
+    $this->eventDispatcher->expects($this->never())
+      ->method('dispatch');
+
+    $this->eventStorage = new EventStorageService($this->tempStore, $this->eventDispatcher);
+
+    $this->eventStorage->addEvent($this->event);
+  }
+
+}