diff --git a/modules/order/commerce_order.post_update.php b/modules/order/commerce_order.post_update.php
index 26dd36ceba..313331df45 100644
--- a/modules/order/commerce_order.post_update.php
+++ b/modules/order/commerce_order.post_update.php
@@ -5,6 +5,7 @@
  * Post update functions for Order.
  */
 
+use Drupal\Core\Field\BaseFieldDefinition;
 use Drupal\Core\Entity\Entity\EntityFormDisplay;
 
 /**
@@ -158,7 +159,8 @@ function commerce_order_post_update_5() {
 function commerce_order_post_update_6() {
   // Remove the default_country setting from any profile form.
   // That allows Commerce to apply its own default taken from the store.
-  $query = \Drupal::entityQuery('entity_form_display')->condition('targetEntityType', 'profile');
+  $query = \Drupal::entityQuery('entity_form_display')
+    ->condition('targetEntityType', 'profile');
   $ids = $query->execute();
   $form_displays = EntityFormDisplay::loadMultiple($ids);
   foreach ($form_displays as $id => $form_display) {
@@ -170,3 +172,18 @@ function commerce_order_post_update_6() {
     }
   }
 }
+
+/**
+ * Add 'total_paid' field to 'commerce_order' entities.
+ */
+function commerce_order_post_update_7() {
+  $storage_definition = BaseFieldDefinition::create('commerce_price')
+    ->setLabel(t('Total paid'))
+    ->setDescription(t('The total amount paid on the order.'))
+    ->setReadOnly(TRUE)
+    ->setDisplayConfigurable('form', FALSE)
+    ->setDisplayConfigurable('view', TRUE);
+  \Drupal::entityDefinitionUpdateManager()
+    ->installFieldStorageDefinition('total_paid', 'commerce_order', 'commerce_order', $storage_definition);
+  return t('The order total paid field was created.');
+}
diff --git a/modules/order/src/Entity/Order.php b/modules/order/src/Entity/Order.php
index 99eb6bef5d..d95659de00 100644
--- a/modules/order/src/Entity/Order.php
+++ b/modules/order/src/Entity/Order.php
@@ -4,6 +4,7 @@
 
 use Drupal\commerce\Entity\CommerceContentEntityBase;
 use Drupal\commerce_order\Adjustment;
+use Drupal\commerce_price\Price;
 use Drupal\commerce_store\Entity\StoreInterface;
 use Drupal\Core\Entity\EntityChangedTrait;
 use Drupal\Core\Entity\EntityStorageInterface;
@@ -390,6 +391,49 @@ public function getTotalPrice() {
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function addPayment(Price $amount) {
+    $this->setTotalPaid($this->getTotalPaid()->add($amount));
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function subtractPayment(Price $amount) {
+    $this->setTotalPaid($this->getTotalPaid()->subtract($amount));
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTotalPaid() {
+    if (!$this->get('total_paid')->isEmpty()) {
+      return $this->get('total_paid')->first()->toPrice();
+    }
+    return new Price('0', $this->getStore()->getDefaultCurrencyCode());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setTotalPaid(Price $amount) {
+    $this->set('total_paid', $amount);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getBalance() {
+    if ($this->getTotalPrice() && $this->getTotalPaid()) {
+      return $this->getTotalPrice()->subtract($this->getTotalPaid());
+    }
+    return $this->getTotalPrice();
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -671,6 +715,13 @@ public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
       ->setDisplayConfigurable('form', FALSE)
       ->setDisplayConfigurable('view', TRUE);
 
+    $fields['total_paid'] = BaseFieldDefinition::create('commerce_price')
+      ->setLabel(t('Total paid'))
+      ->setDescription(t('The total amount paid on the order.'))
+      ->setReadOnly(TRUE)
+      ->setDisplayConfigurable('form', FALSE)
+      ->setDisplayConfigurable('view', TRUE);
+
     $fields['state'] = BaseFieldDefinition::create('state')
       ->setLabel(t('State'))
       ->setDescription(t('The order state.'))
diff --git a/modules/order/src/Entity/OrderInterface.php b/modules/order/src/Entity/OrderInterface.php
index ba21dc201d..1edd1e57d1 100644
--- a/modules/order/src/Entity/OrderInterface.php
+++ b/modules/order/src/Entity/OrderInterface.php
@@ -3,6 +3,7 @@
 namespace Drupal\commerce_order\Entity;
 
 use Drupal\commerce_order\EntityAdjustableInterface;
+use Drupal\commerce_price\Price;
 use Drupal\commerce_store\Entity\StoreInterface;
 use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\EntityChangedInterface;
@@ -272,6 +273,50 @@ public function recalculateTotalPrice();
    */
   public function getTotalPrice();
 
+  /**
+   * Adds an amount to the order total paid.
+   *
+   * @param \Drupal\commerce_price\Price $amount
+   *   The amount to add to the total paid.
+   *
+   * @return $this
+   */
+  public function addPayment(Price $amount);
+
+  /**
+   * Subtracts an amount from the order total paid.
+   *
+   * @param \Drupal\commerce_price\Price $amount
+   *   The amount to subtract from the total paid.
+   *
+   * @return $this
+   */
+  public function subtractPayment(Price $amount);
+
+  /**
+   * Gets the total amount paid on the order.
+   *
+   * @return \Drupal\commerce_price\Price
+   *   The order total paid amount.
+   */
+  public function getTotalPaid();
+
+  /**
+   * Sets the total amount paid on the order.
+   *
+   * @param \Drupal\commerce_price\Price $amount
+   *   The amount to set as the order total paid.
+   */
+  public function setTotalPaid(Price $amount);
+
+  /**
+   * Gets the amount unpaid on the order.
+   *
+   * @return \Drupal\commerce_price\Price|null
+   *   The total order amount minus the total paid, or NULL.
+   */
+  public function getBalance();
+
   /**
    * Gets the order state.
    *
diff --git a/modules/order/tests/src/Kernel/Entity/OrderTest.php b/modules/order/tests/src/Kernel/Entity/OrderTest.php
index a7bff3d94b..420e506dc1 100644
--- a/modules/order/tests/src/Kernel/Entity/OrderTest.php
+++ b/modules/order/tests/src/Kernel/Entity/OrderTest.php
@@ -8,6 +8,8 @@
 use Drupal\commerce_order\Entity\OrderItemType;
 use Drupal\commerce_price\Exception\CurrencyMismatchException;
 use Drupal\commerce_price\Price;
+use Drupal\commerce_payment\Entity\Payment;
+use Drupal\commerce_payment\Entity\PaymentGateway;
 use Drupal\profile\Entity\Profile;
 use Drupal\Tests\commerce\Kernel\CommerceKernelTestBase;
 
@@ -27,6 +29,13 @@ class OrderTest extends CommerceKernelTestBase {
    */
   protected $user;
 
+  /**
+   * The payment gateway plugin.
+   *
+   * @var \Drupal\commerce_payment\Plugin\Commerce\PaymentGateway\SupportsRefundsInterface
+   */
+  protected $payment_gateway_plugin;
+
   /**
    * Modules to enable.
    *
@@ -36,6 +45,8 @@ class OrderTest extends CommerceKernelTestBase {
     'entity_reference_revisions',
     'profile',
     'state_machine',
+    'commerce_payment',
+    'commerce_payment_example',
     'commerce_product',
     'commerce_order',
   ];
@@ -49,6 +60,7 @@ protected function setUp() {
     $this->installEntitySchema('profile');
     $this->installEntitySchema('commerce_order');
     $this->installEntitySchema('commerce_order_item');
+    $this->installEntitySchema('commerce_payment');
     $this->installConfig('commerce_order');
 
     // An order item type that doesn't need a purchasable entity, for simplicity.
@@ -58,6 +70,14 @@ protected function setUp() {
       'orderType' => 'default',
     ])->save();
 
+    $payment_gateway = PaymentGateway::create([
+      'id' => 'example',
+      'label' => 'Example',
+      'plugin' => 'example_onsite',
+    ]);
+    $payment_gateway->save();
+    $this->payment_gateway_plugin = $payment_gateway->getPlugin();
+
     $user = $this->createUser();
     $this->user = $this->reloadEntity($user);
   }
@@ -96,6 +116,11 @@ protected function setUp() {
    * @covers ::getSubtotalPrice
    * @covers ::recalculateTotalPrice
    * @covers ::getTotalPrice
+   * @covers ::getBalance
+   * @covers ::addPayment
+   * @covers ::subtractPayment
+   * @covers ::setTotalPaid
+   * @covers ::getTotalPaid
    * @covers ::getState
    * @covers ::getRefreshState
    * @covers ::setRefreshState
@@ -138,6 +163,7 @@ public function testOrder() {
     $order = Order::create([
       'type' => 'default',
       'state' => 'completed',
+      'store_id' => $this->store->id(),
     ]);
     $order->save();
 
@@ -183,6 +209,7 @@ public function testOrder() {
     $this->assertNotEmpty($order->hasItem($another_order_item));
 
     $this->assertEquals(new Price('8.00', 'USD'), $order->getTotalPrice());
+    $this->assertEquals(new Price('8.00', 'USD'), $order->getBalance());
     $adjustments = [];
     $adjustments[] = new Adjustment([
       'type' => 'custom',
@@ -213,6 +240,7 @@ public function testOrder() {
     $order->removeAdjustment($adjustments[0]);
     $this->assertEquals(new Price('8.00', 'USD'), $order->getSubtotalPrice());
     $this->assertEquals(new Price('18.00', 'USD'), $order->getTotalPrice());
+    $this->assertEquals(new Price('18.00', 'USD'), $order->getBalance());
     $this->assertEquals([$adjustments[1], $adjustments[2]], $order->getAdjustments());
     $order->setAdjustments($adjustments);
     $this->assertEquals($adjustments, $order->getAdjustments());
@@ -258,6 +286,71 @@ public function testOrder() {
     unset($multiplied_order_item_adjustments[0]);
     $this->assertEquals(array_merge($multiplied_order_item_adjustments, $adjustments), $order->collectAdjustments());
 
+    $this->assertEquals(new Price('31.00', 'USD'), $order->getTotalPrice());
+    $this->assertEquals(new Price('31.00', 'USD'), $order->getBalance());
+
+    // Test that payments update the order total paid and balance.
+    $order->save();
+    $payment = Payment::create([
+      'order_id' => $order->id(),
+      'amount' => new Price('29.00', 'USD'),
+      'payment_gateway' => 'example',
+      'state' => 'completed',
+    ]);
+    $payment->save();
+    $order = Order::load($order->id());
+    $this->assertEquals(new Price('2.00', 'USD'), $order->getBalance());
+    $this->payment_gateway_plugin->refundPayment($payment, new Price('5.00', 'USD'));
+    $order = Order::load($order->id());
+    $this->assertEquals(new Price('7.00', 'USD'), $order->getBalance());
+    $payment->delete();
+    $order = Order::load($order->id());
+    $this->assertEquals(new Price('31.00', 'USD'), $order->getBalance());
+    $payment2 = Payment::create([
+      'order_id' => $order->id(),
+      'amount' => new Price('31.00', 'USD'),
+      'payment_gateway' => 'example',
+      'state' => 'completed',
+    ]);
+    $payment2->save();
+    $order = Order::load($order->id());
+    $this->assertEquals(new Price('0.00', 'USD'), $order->getBalance());
+
+    // Test that payments can be partially refunded multiple times.
+    $this->payment_gateway_plugin->refundPayment($payment2, new Price('17.00', 'USD'));
+    $order = Order::load($order->id());
+    $this->assertEquals(new Price('17.00', 'USD'), $order->getBalance());
+    $this->payment_gateway_plugin->refundPayment($payment2, new Price('5.00', 'USD'));
+    $order = Order::load($order->id());
+    $this->assertEquals(new Price('22.00', 'USD'), $order->getBalance());
+
+    // Test that the total paid amount can be set explicitly on the order.
+    $order->setTotalPaid(new Price('0.00', 'USD'));
+    $order->save();
+    $this->assertEquals(new Price('31.00', 'USD'), $order->getBalance());
+
+    // Test that payments only substract total when setting to completed.
+    $order->save();
+    $payment = Payment::create([
+      'order_id' => $order->id(),
+      'amount' => new Price('25.00', 'USD'),
+      'payment_gateway' => 'example',
+    ]);
+    $payment->save();
+    $order = Order::load($order->id());
+    $this->assertEquals(new Price('0.00', 'USD'), $order->getTotalPaid());
+
+    $payment->setState('completed');
+    $payment->save();
+    $order = Order::load($order->id());
+    $this->assertEquals(new Price('25.00', 'USD'), $order->getTotalPaid());
+    $this->assertEquals(new Price('6.00', 'USD'), $order->getBalance());
+
+    // Test that deleted payments update the order total paid and balance.
+    $payment->delete();
+    $order = Order::load($order->id());
+    $this->assertEquals(new Price('0.00', 'USD'), $order->getTotalPaid());
+
     $this->assertEquals('completed', $order->getState()->value);
 
     $order->setRefreshState(Order::REFRESH_ON_SAVE);
diff --git a/modules/payment/src/Entity/Payment.php b/modules/payment/src/Entity/Payment.php
index f887f6f957..d7a5eab6db 100644
--- a/modules/payment/src/Entity/Payment.php
+++ b/modules/payment/src/Entity/Payment.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\commerce_payment\Entity;
 
+use Drupal\commerce_payment\Event\PaymentEvents;
+use Drupal\commerce_payment\PaymentStorage;
 use Drupal\commerce_price\Price;
 use Drupal\Core\Entity\ContentEntityBase;
 use Drupal\Core\Entity\EntityMalformedException;
@@ -290,7 +292,8 @@ public function preSave(EntityStorageInterface $storage) {
       $refunded_amount = new Price('0', $this->getAmount()->getCurrencyCode());
       $this->setRefundedAmount($refunded_amount);
     }
-    // Maintain the authorized completed timestamps.
+    // Maintain the authorized completed timestamps while also maintaining the
+    // order balance.
     $state = $this->getState()->value;
     $original_state = isset($this->original) ? $this->original->getState()->value : '';
     if ($state == 'authorized' && $original_state != 'authorized') {
@@ -299,9 +302,33 @@ public function preSave(EntityStorageInterface $storage) {
       }
     }
     if ($state == 'completed' && $original_state != 'completed') {
+      $this->getOrder()->addPayment($this->getAmount())->save();
       if (empty($this->getCompletedTime())) {
         $this->setCompletedTime(\Drupal::time()->getRequestTime());
       }
+      if ($this->getOrder()->getBalance()->isZero() && $storage instanceof PaymentStorage) {
+        $storage->dispatchPaymentEvent($this, PaymentEvents::PAYMENT_ORDER_PAID_IN_FULL);
+      }
+    }
+    elseif (in_array($state, ['partially_refunded', 'refunded']) &&
+        in_array($original_state, ['completed', 'partially_refunded'])) {
+      $original = $this->values['original'];
+      $net_refund = $this->getRefundedAmount()->subtract($original->getRefundedAmount());
+      $this->getOrder()->subtractPayment($net_refund)->save();
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function preDelete(EntityStorageInterface $storage, array $entities) {
+    parent::preDelete($storage, $entities);
+
+    // Subtract each payment from order.
+    foreach ($entities as $payment) {
+      $net_payment = $payment->getAmount()
+        ->subtract($payment->getRefundedAmount());
+      $payment->getOrder()->subtractPayment($net_payment)->save();
     }
   }
 
diff --git a/modules/payment/src/Event/PaymentEvent.php b/modules/payment/src/Event/PaymentEvent.php
new file mode 100644
index 0000000000..fec57891ec
--- /dev/null
+++ b/modules/payment/src/Event/PaymentEvent.php
@@ -0,0 +1,42 @@
+<?php
+
+namespace Drupal\commerce_payment\Event;
+
+use Drupal\commerce_payment\Entity\PaymentInterface;
+use Symfony\Component\EventDispatcher\Event;
+
+/**
+ * Defines the payment event.
+ *
+ * @see \Drupal\commerce_payment\Event\PaymentEvents
+ */
+class PaymentEvent extends Event {
+
+  /**
+   * The payment.
+   *
+   * @var \Drupal\commerce_payment\Entity\PaymentInterface
+   */
+  protected $payment;
+
+  /**
+   * Constructs a new Paymentevent.
+   *
+   * @param \Drupal\commerce_payment\Entity\PaymentInterface $payment
+   *   The payment.
+   */
+  public function __construct(PaymentInterface $payment) {
+    $this->payment = $payment;
+  }
+
+  /**
+   * Gets the payment.
+   *
+   * @return \Drupal\commerce_payment\Entity\PaymentInterface
+   *   Gets the payment.
+   */
+  public function getEntity() {
+    return $this->payment;
+  }
+
+}
diff --git a/modules/payment/src/Event/PaymentEvents.php b/modules/payment/src/Event/PaymentEvents.php
index 9a4abfeab3..91fb47b0bc 100644
--- a/modules/payment/src/Event/PaymentEvents.php
+++ b/modules/payment/src/Event/PaymentEvents.php
@@ -13,4 +13,13 @@ final class PaymentEvents {
    */
   const FILTER_PAYMENT_GATEWAYS = 'commerce_payment.filter_payment_gateways';
 
+  /**
+   * Name of the event fired after paying an order in full.
+   *
+   * @Event
+   *
+   * @see \Drupal\commerce_payment\Event\PaymentEvent
+   */
+  const PAYMENT_ORDER_PAID_IN_FULL = 'commerce_payment.order_paid_in_full';
+
 }
diff --git a/modules/payment/src/PaymentStorage.php b/modules/payment/src/PaymentStorage.php
index f59d567fed..b7663943bf 100644
--- a/modules/payment/src/PaymentStorage.php
+++ b/modules/payment/src/PaymentStorage.php
@@ -4,6 +4,8 @@
 
 use Drupal\commerce\CommerceContentEntityStorage;
 use Drupal\commerce_order\Entity\OrderInterface;
+use Drupal\commerce_payment\Entity\PaymentInterface;
+use Drupal\commerce_payment\Event\PaymentEvent;
 use Drupal\Core\Entity\EntityStorageException;
 
 /**
@@ -56,4 +58,18 @@ protected function doCreate(array $values) {
     return parent::doCreate($values);
   }
 
+  /**
+   * Notifies other modules about payment events.
+   *
+   * @param \Drupal\commerce_payment\Entity\PaymentInterface $payment
+   *   The payment.
+   * @param string $event_id
+   *   The event identifier defined in
+   *   \Drupal\commerce_payment\Event\PaymentEvents.
+   */
+  public function dispatchPaymentEvent(PaymentInterface $payment, $event_id) {
+    $event = new PaymentEvent($payment);
+    $this->eventDispatcher->dispatch($event_id, $event);
+  }
+
 }
diff --git a/modules/payment/tests/modules/payment_events_test/payment_events_test.info.yml b/modules/payment/tests/modules/payment_events_test/payment_events_test.info.yml
new file mode 100644
index 0000000000..604ef369cc
--- /dev/null
+++ b/modules/payment/tests/modules/payment_events_test/payment_events_test.info.yml
@@ -0,0 +1,4 @@
+name: 'Configuration events test'
+type: module
+package: Testing
+core: 8.x
diff --git a/modules/payment/tests/modules/payment_events_test/payment_events_test.services.yml b/modules/payment/tests/modules/payment_events_test/payment_events_test.services.yml
new file mode 100644
index 0000000000..a7df3aa96c
--- /dev/null
+++ b/modules/payment/tests/modules/payment_events_test/payment_events_test.services.yml
@@ -0,0 +1,6 @@
+services:
+  payment_events_test.event_subscriber:
+    class: Drupal\payment_events_test\EventSubscriber
+    arguments: ['@state']
+    tags:
+      - { name: event_subscriber }
diff --git a/modules/payment/tests/modules/payment_events_test/src/EventSubscriber.php b/modules/payment/tests/modules/payment_events_test/src/EventSubscriber.php
new file mode 100644
index 0000000000..fb49a6d3dd
--- /dev/null
+++ b/modules/payment/tests/modules/payment_events_test/src/EventSubscriber.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace Drupal\payment_events_test;
+
+use Drupal\commerce_payment\Event\PaymentEvent;
+use Drupal\commerce_payment\Event\PaymentEvents;
+use Drupal\Core\State\StateInterface;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+class EventSubscriber implements EventSubscriberInterface {
+
+  /**
+   * The state key value store.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * Constructs the Event Subscriber object.
+   *
+   * @param \Drupal\Core\State\StateInterface $state
+   *   The state key value store.
+   */
+  public function __construct(StateInterface $state) {
+    $this->state = $state;
+  }
+
+  /**
+   * Reacts to payment event.
+   *
+   * @param \Drupal\commerce_payment\Event\PaymentEvent $event
+   *   The payment event.
+   * @param string $name
+   *   The name of the event.
+   */
+  public function paymentEvent(PaymentEvent $event, $name) {
+    $this->state->set('payment_events_test.event', [
+      'event_name' => $name,
+      'event_entity' => $event->getEntity(),
+    ]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    $events[PaymentEvents::PAYMENT_ORDER_PAID_IN_FULL][] = ['paymentEvent'];
+    return $events;
+  }
+
+}
diff --git a/modules/payment/tests/src/Kernel/PaymentEventsTest.php b/modules/payment/tests/src/Kernel/PaymentEventsTest.php
new file mode 100644
index 0000000000..fa131e9a1a
--- /dev/null
+++ b/modules/payment/tests/src/Kernel/PaymentEventsTest.php
@@ -0,0 +1,127 @@
+<?php
+
+namespace Drupal\Tests\commerce_payment\Kernel;
+
+use Drupal\commerce_order\Entity\Order;
+use Drupal\commerce_order\Entity\OrderItem;
+use Drupal\commerce_order\Entity\OrderItemType;
+use Drupal\commerce_payment\Entity\Payment;
+use Drupal\commerce_payment\Entity\PaymentGateway;
+use Drupal\commerce_payment\Entity\PaymentMethod;
+use Drupal\commerce_payment\Event\PaymentEvents;
+use Drupal\commerce_price\Price;
+use Drupal\Tests\commerce\Kernel\CommerceKernelTestBase;
+
+/**
+ * Tests the payment events.
+ *
+ * @group commerce
+ */
+class PaymentEventsTest extends CommerceKernelTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = [
+    'address',
+    'entity_reference_revisions',
+    'profile',
+    'state_machine',
+    'commerce_product',
+    'commerce_order',
+    'commerce_payment',
+    'commerce_payment_example',
+    'payment_events_test',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installEntitySchema('profile');
+    $this->installEntitySchema('commerce_order');
+    $this->installEntitySchema('commerce_order_item');
+    $this->installEntitySchema('commerce_payment');
+    $this->installEntitySchema('commerce_payment_method');
+    $this->installConfig('commerce_order');
+    $this->installConfig('commerce_payment');
+
+    // An order item type that doesn't need a purchasable entity, for simplicity.
+    OrderItemType::create([
+      'id' => 'test',
+      'label' => 'Test',
+      'orderType' => 'default',
+    ])->save();
+
+    $payment_gateway = PaymentGateway::create([
+      'id' => 'example',
+      'label' => 'Example',
+      'plugin' => 'example_onsite',
+    ]);
+    $payment_gateway->save();
+
+    $user = $this->createUser();
+
+    /** @var \Drupal\commerce_payment\Entity\PaymentMethodInterface $payment_method */
+    $payment_method_active = PaymentMethod::create([
+      'type' => 'credit_card',
+      'payment_gateway' => 'example',
+      // Thu, 16 Jan 2020.
+      'expires' => '1579132800',
+      'uid' => $user->id(),
+    ]);
+    $payment_method_active->save();
+  }
+
+  /**
+   * Tests the basic payment events.
+   */
+  public function testPaymentEvents() {
+    /** @var \Drupal\commerce_order\Entity\OrderItemInterface $order_item */
+    $order_item = OrderItem::create([
+      'type' => 'test',
+      'quantity' => '1',
+      'unit_price' => new Price('39.99', 'USD'),
+    ]);
+    $order_item->save();
+    $order_item = $this->reloadEntity($order_item);
+    $order = Order::create([
+      'type' => 'default',
+      'state' => 'completed',
+      'store_id' => $this->store->id(),
+    ]);
+    $order->setItems([$order_item]);
+    $order->save();
+
+    $this->assertEquals(new Price('39.99', 'USD'), $order->getTotalPrice());
+    $this->assertEquals(new Price('39.99', 'USD'), $order->getBalance());
+
+    // Create a dummy payment.
+    $payment = Payment::create([
+      'order_id' => $order->id(),
+      'payment_gateway' => 'example',
+      'payment_method' => 'credit_card',
+      'remote_id' => '123456',
+      'amount' => [
+        'number' => '39.99',
+        'currency_code' => 'USD',
+      ],
+      'state' => 'completed',
+      'test' => TRUE,
+    ]);
+    $payment->save();
+
+    $order = $this->reloadEntity($order);
+    $this->assertEquals(new Price('0.00', 'USD'), $order->getBalance());
+
+    // Check the paid in full event.
+    $event_recorder = \Drupal::state()->get('payment_events_test.event', FALSE);
+    $this->assertEquals(PaymentEvents::PAYMENT_ORDER_PAID_IN_FULL, $event_recorder['event_name']);
+    $this->assertEquals($payment->id(), $event_recorder['event_entity']->id());
+  }
+
+}