>>> from box import Box
>>> b = Box(0, 0, 100, 100)
>>> b.width
100
>>> b.height
100
>>> b.aspect_ratio()
1.0
>>> str(b)
'(0.00, 0.00, 100.00, 100.00)'
>>> b2 = Box(0, 0, 50, 100)
>>> b2.aspect_ratio()
0.5
>>> b3 = Box(0, 0, 100, 20)
>>> b3.aspect_ratio()
5.0

Test of fitting_window
Should pass after implementation

>>> b10 = b.fitting_window(0.5)
>>> b10.height
200.0
>>> b10.ymin
-50.0

>>> b4 = b3.fitting_window(1.0)
>>> b4.width
100
>>> b4.height
100.0
>>> b4.xmin
0
>>> b4.ymin
-40.0
>>> b5 = b2.fitting_window(1.0)
>>> b5.width
100.0
>>> b5.xmin
-25.0