ManageTest.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

namespace Magento\Newsletter\Controller;

/**
 * @magentoDbIsolation enabled
 */
class ManageTest extends \Magento\TestFramework\TestCase\AbstractController
{
    /**
     * @var \Magento\Customer\Model\Session
     */
    protected $customerSession;

    /**
     * @var \Magento\Framework\Session\Generic
     */
    protected $coreSession;

    /**
     * Test setup
     */
    protected function setUp()
    {
        parent::setUp();
        $objectManager = \Magento\TestFramework\Helper\Bootstrap::getObjectManager();
        $this->customerSession = $objectManager->get(\Magento\Customer\Model\Session::class);
        $this->customerSession->setCustomerId(1);
        $this->coreSession = $objectManager->get(\Magento\Framework\Session\Generic::class);
        $this->coreSession->setData('_form_key', 'formKey');
    }

    /**
     * test tearDown
     */
    protected function tearDown()
    {
        $this->customerSession->setCustomerId(null);
        $this->coreSession->unsetData('_form_key');
    }

    /**
     * @magentoDataFixture Magento/Customer/_files/customer.php
     */
    public function testSaveAction()
    {
        $this->getRequest()
            ->setParam('form_key', 'formKey')
            ->setParam('is_subscribed', '1');
        $this->dispatch('newsletter/manage/save');

        $this->assertRedirect($this->stringContains('customer/account/'));

        /**
         * Check that errors
         */
        $this->assertSessionMessages($this->isEmpty(), \Magento\Framework\Message\MessageInterface::TYPE_ERROR);

        /**
         * Check that success message
         */
        $this->assertSessionMessages(
            $this->equalTo(['We have saved your subscription.']),
            \Magento\Framework\Message\MessageInterface::TYPE_SUCCESS
        );
    }

    /**
     * @magentoDataFixture Magento/Customer/_files/customer.php
     */
    public function testSaveActionRemoveSubscription()
    {

        $this->getRequest()
            ->setParam('form_key', 'formKey')
            ->setParam('is_subscribed', '0');
        $this->dispatch('newsletter/manage/save');

        $this->assertRedirect($this->stringContains('customer/account/'));

        /**
         * Check that errors
         */
        $this->assertSessionMessages($this->isEmpty(), \Magento\Framework\Message\MessageInterface::TYPE_ERROR);

        /**
         * Check that success message
         */
        $this->assertSessionMessages(
            $this->equalTo(['We have updated your subscription.']),
            \Magento\Framework\Message\MessageInterface::TYPE_SUCCESS
        );
    }
}