public function testItCanCalculateArea()
{
$circle = new Sphere(0);
$this->assertEquals(0, $circle->area());
$circle = new Sphere(2);
$value = 4 * pi() * pow(2, 2);
$this->assertEquals($value, $circle->area());
$circle = new Sphere(3.14);
$value = 4 * pi() * pow(3.14, 2);
$this->assertEquals($value, $circle->area());
}
