InfoTest.php

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

class InfoTest extends \PHPUnit\Framework\TestCase
{
    /**
     * @magentoConfigFixture current_store payment/banktransfer/title Bank Method Title
     * @magentoConfigFixture current_store payment/checkmo/title Checkmo Title Of The Method
     * @magentoAppArea adminhtml
     */
    public function testGetChildPdfAsArray()
    {
        /** @var $layout \Magento\Framework\View\Layout */
        $layout = \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->get(
            \Magento\Framework\View\LayoutInterface::class
        );
        $block = $layout->createBlock(\Magento\Payment\Block\Info::class, 'block');

        /** @var $paymentInfoBank \Magento\Payment\Model\Info  */
        $paymentInfoBank = \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->create(
            \Magento\Payment\Model\Info::class
        );
        $paymentInfoBank->setMethodInstance(
            \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->create(
                \Magento\OfflinePayments\Model\Banktransfer::class
            )
        );
        /** @var $childBank \Magento\Payment\Block\Info\Instructions */
        $childBank = $layout->addBlock(\Magento\Payment\Block\Info\Instructions::class, 'child.one', 'block');
        $childBank->setInfo($paymentInfoBank);

        $nonExpectedHtml = 'non-expected html';
        $childHtml = $layout->addBlock(\Magento\Framework\View\Element\Text::class, 'child.html', 'block');
        $childHtml->setText($nonExpectedHtml);

        /** @var $paymentInfoCheckmo \Magento\Payment\Model\Info */
        $paymentInfoCheckmo = \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->create(
            \Magento\Payment\Model\Info::class
        );
        $paymentInfoCheckmo->setMethodInstance(
            \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->create(
                \Magento\OfflinePayments\Model\Checkmo::class
            )
        );
        /** @var $childCheckmo \Magento\OfflinePayments\Block\Info\Checkmo */
        $childCheckmo = $layout->addBlock(
            \Magento\OfflinePayments\Block\Info\Checkmo::class,
            'child.just.another',
            'block'
        );
        $childCheckmo->setInfo($paymentInfoCheckmo);

        $pdfArray = $block->getChildPdfAsArray();

        $this->assertInternalType('array', $pdfArray);
        $this->assertCount(2, $pdfArray);
        $text = implode('', $pdfArray);
        $this->assertContains('Bank Method Title', $text);
        $this->assertContains('Checkmo Title Of The Method', $text);
        $this->assertNotContains($nonExpectedHtml, $text);
    }
}