public function canModifyVariablesSelectively()
{
$mock = $this->getMock($this->createInstanceClassName(), array('dummy'));
$mock->setVariables(array('foo' => 'baz', 'abc' => 'xyz'));
$properties = array('options' => array('foo' => 'bar'));
$mock->modify($properties);
$this->assertEquals('bar', $mock->getVariable('foo'));
$this->assertEquals('xyz', $mock->getVariable('abc'));
}