>>> from patients11 import filter_fever_interval

>>> r = filter_fever_interval('pats1.txt', 'pats1in.txt', 'pats1out.txt', 37.0, 38.0)

>>> with open('pats1in.txt', 'r') as f, open('pats1in-37.0-38.0.txt', 'r') as fref:
... 	l = f.readline()
... 	lref = fref.readline()
... 	while l != '' and lref == l:
... 		l = f.readline()
... 		lref = fref.readline()
... 	igualsin = lref == l == ''

>>> with open('pats1out.txt', 'r') as f, open('pats1out-37.0-38.0.txt',  'r') as fref:
... 	l = f.readline()
... 	lref = fref.readline()
... 	while l != '' and lref == l:
... 		l = f.readline()
... 		lref = fref.readline()
... 	igualsout = lref == l == ''

>>> r == (9, 4, 5) and igualsin and igualsout
True