ConfigTest.php

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

class ConfigTest extends \PHPUnit\Framework\TestCase
{
    /**
     * @var \Magento\Tax\Model\Config
     */
    protected $_model = null;

    protected function setUp()
    {
        $this->_model = \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->create(
            \Magento\Tax\Model\Config::class
        );
    }

    public function testSetPriceIncludesTax()
    {
        $this->assertFalse($this->_model->priceIncludesTax());
        $this->assertSame($this->_model, $this->_model->setPriceIncludesTax(1));
        $this->assertTrue($this->_model->priceIncludesTax());
        $this->_model->setPriceIncludesTax(null);
        $this->assertFalse($this->_model->priceIncludesTax());
    }

    /**
     * @magentoConfigFixture current_store tax/calculation/price_includes_tax 1
     */
    public function testPriceIncludesTaxNonDefault()
    {
        $this->assertTrue($this->_model->priceIncludesTax());
    }
}