public function testGetCustomerTaxClassId()
{
$groupId = 1;
$taxClassId = 1;
$customerGroupMock = $this->getMockBuilder('Magento\\Customer\\Service\\V1\\Data\\CustomerGroup')->disableOriginalConstructor()->getMock();
$customerGroupMock->expects($this->once())->method('getTaxClassId')->will($this->returnValue($taxClassId));
$this->customerGroupServiceMock->expects($this->once())->method('getGroup')->with($groupId)->will($this->returnValue($customerGroupMock));
$this->quote->setData('customer_group_id', $groupId);
$result = $this->quote->getCustomerTaxClassId();
$this->assertEquals($taxClassId, $result);
}