Adding coverage test cases, fixing Order/Payment/Info that had the same problem.

Author: marcoaacoliveira

app/code/Magento/Sales/Model/Order/Payment/Info.php

@@ -192,6 +192,7 @@ public function getAdditionalInformation($key = null)
      */
     public function unsAdditionalInformation($key = null)
     {
+        $this->initAdditionalInformation();
         if ($key && isset($this->additionalInformation[$key])) {
             unset($this->additionalInformation[$key]);
             return $this->setData('additional_information', $this->additionalInformation);

dev/tests/integration/testsuite/Magento/Payment/Model/PaymentInfoTest.php

@@ -0,0 +1,64 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+namespace Magento\Payment\Model;
+
+use Magento\Sales\Model\Order;
+use Magento\Quote\Model\Quote;
+use Magento\TestFramework\Helper\Bootstrap;
+use Magento\TestFramework\ObjectManager;
+
+/**
+ * @magentoAppArea adminhtml
+ * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
+ */
+class PaymentInfoTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @var ObjectManager
+     */
+    protected $_objectManager;
+
+    /**
+     * @var Order
+     */
+    protected $_order;
+
+    /** @var Quote */
+    protected $_quote;
+
+    protected function setUp()
+    {
+        $this->_objectManager = Bootstrap::getObjectManager();
+        $this->_order = $this->_objectManager->create(
+            Order::class
+        );
+        $this->_quote = $this->_objectManager->create(
+            Quote::class
+        );
+    }
+
+    /**
+     * @magentoDbIsolation enabled
+     * @magentoAppIsolation enabled
+     * @magentoDataFixture Magento/Payment/_files/payment_info.php
+     */
+    public function testUnsetPaymentInformation()
+    {
+        $order = $this->_order->loadByIncrementId('100000001');
+        /** @var \Magento\Sales\Model\Order\Payment $paymentOrder */
+        $paymentOrder = $order->getPayment();
+        $paymentOrder->unsAdditionalInformation('testing');
+
+        $quote = $this->_quote->load('reserved_order_id', 'reserved_order_id');
+        /** @var \Magento\Quote\Model\Quote\Payment $paymentQuote */
+        $paymentQuote = $quote->getPayment();
+        $paymentQuote->unsAdditionalInformation('testing');
+
+
+        $this->assertFalse($paymentOrder->hasAdditionalInformation('testing'));
+        $this->assertFalse($paymentQuote->hasAdditionalInformation('testing'));
+    }
+}

dev/tests/integration/testsuite/Magento/Payment/_files/payment_info.php

@@ -0,0 +1,83 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+use Magento\Quote\Api\CartRepositoryInterface;
+use Magento\TestFramework\Helper\Bootstrap;
+use Magento\Sales\Model\Order\Address;
+use Magento\Sales\Model\Order\Payment;
+use Magento\Paypal\Model\Config;
+use Magento\Sales\Model\Order;
+use Magento\Quote\Model\Quote;
+use Magento\Quote\Model\Quote\Payment as PaymentQuote;
+
+/** @var $objectManager \Magento\TestFramework\ObjectManager */
+$objectManager = Bootstrap::getObjectManager();
+
+$addressData = [
+    'firstname' => 'guest',
+    'lastname' => 'guest',
+    'email' => '[email protected]',
+    'street' => 'street',
+    'city' => 'Los Angeles',
+    'region' => 'CA',
+    'postcode' => '1',
+    'country_id' => 'US',
+    'telephone' => '1'
+];
+$billingAddress = $objectManager->create(
+    Address::class,
+    ['data' => $addressData]
+);
+$billingAddress->setAddressType('billing');
+$shippingAddress = clone $billingAddress;
+$shippingAddress->setId(null)->setAddressType('shipping');
+
+/** @var Payment $paymentOrder */
+$paymentOrder = $objectManager->create(
+    Payment::class
+);
+
+$paymentOrder->setMethod(Config::METHOD_WPP_EXPRESS);
+$paymentOrder->setAdditionalInformation('testing', 'testing additional data');
+
+$amount = 100;
+
+/** @var Order $order */
+$order = $objectManager->create(Order::class);
+$order->setCustomerEmail('[email protected]')
+    ->setIncrementId('100000001')
+    ->setSubtotal($amount)
+    ->setBaseSubtotal($amount)
+    ->setBaseGrandTotal($amount)
+    ->setGrandTotal($amount)
+    ->setBaseCurrencyCode('USD')
+    ->setCustomerIsGuest(true)
+    ->setStoreId(1)
+    ->setEmailSent(true)
+    ->setBillingAddress($billingAddress)
+    ->setShippingAddress($shippingAddress)
+    ->setPayment($paymentOrder);
+$order->save();
+
+
+
+/** @var Quote $quote */
+$quote = $objectManager->create(Quote::class);
+$quote->setStoreId(1)
+    ->setIsActive(true)
+    ->setIsMultiShipping(false)
+    ->setReservedOrderId('reserved_order_id');
+
+$quote->getPayment()
+    ->setMethod(Config::METHOD_WPP_EXPRESS)
+    ->setAdditionalInformation('testing', 'testing additional data');
+
+$quote->collectTotals();
+
+
+/** @var CartRepositoryInterface $repository */
+$repository = $objectManager->get(CartRepositoryInterface::class);
+$repository->save($quote);