Rectangle / Square LSP Example Violation in PHP

LSPExampleViolation.php

<?php

class Rectangle
{
    private $_width;
    private $_height;

    public function getWidth()
    {
        return $this->_width;
    }

    public function setWidth($width)
    {
        $this->_width = $width;
    }

    public function getHeight()
    {
        return $this->_height;
    }

    public function setHeight($height)
    {
        $this->_height = $height;
    }
}

class Square extends Rectangle
{
    public function setWidth($width)
    {
        parent::setWidth($width);
        parent::setHeight($width);
    }

    public function setHeight($height)
    {
        parent::setWidth($height);
        parent::setHeight($height);
    }
}

class LSPRectangeTest extends PHPUnit_Framework_TestCase
{
    private function areaTest(Rectangle $rectangle)
    {
        $width = 5;
        $height = 4;
        $rectangle->setWidth($width);
        $rectangle->setHeight($height);
        $actualArea = $rectangle->getWidth() * $rectangle->getHeight();
        $expectedArea = $width * $height;
        $this->assertEquals($expectedArea, $actualArea);
    }

    public function testRectangleArea()
    {
        $rectangle = new Rectangle();
        $this->areaTest($rectangle);
    }

    public function testSquareArea()
    {
        $square = new Square();
        $this->areaTest($square);
    }
}