public function testItCanCalculatePerimeter() { $circle = new Circle(0); $this->assertEquals(0, $circle->perimeter()); $circle = new Circle(2); $value = 2 * pi() * 2; $this->assertEquals($value, $circle->perimeter()); $circle = new Circle(3.14); $value = 2 * pi() * 3.14; $this->assertEquals($value, $circle->perimeter()); }