## Function Tests. def f1(): return 'f1' assert f1() == 'f1' def f2(a, b, c, d): return c assert f2('a', 'b', 'c', 'd') == 'c' def f3(a,b): return a - b assert f3(1,2) == -1 def fact(n): if n == 1: return 1 return n * fact(n - 1) assert fact(5)==120