39     assert_eq!(1, pow5_factor(5));  in test_pow5_factor()
52     assert_eq!(2, pow5_factor(5 * 5));  in test_pow5_factor()
53     assert_eq!(3, pow5_factor(5 * 5 * 5));  in test_pow5_factor()
54     assert_eq!(4, pow5_factor(5 * 5 * 5 * 5));  in test_pow5_factor()
55     assert_eq!(5, pow5_factor(5 * 5 * 5 * 5 * 5));  in test_pow5_factor()
56     assert_eq!(6, pow5_factor(5 * 5 * 5 * 5 * 5 * 5));  in test_pow5_factor()
57     assert_eq!(7, pow5_factor(5 * 5 * 5 * 5 * 5 * 5 * 5));  in test_pow5_factor()
58     assert_eq!(8, pow5_factor(5 * 5 * 5 * 5 * 5 * 5 * 5 * 5));  in test_pow5_factor()
59     assert_eq!(9, pow5_factor(5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5));  in test_pow5_factor()
60     assert_eq!(10, pow5_factor(5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5));  in test_pow5_factor()
63     assert_eq!(1, pow5_factor(42 * 5));  in test_pow5_factor()
64     assert_eq!(2, pow5_factor(42 * 5 * 5));  in test_pow5_factor()
65     assert_eq!(3, pow5_factor(42 * 5 * 5 * 5));  in test_pow5_factor()
66     assert_eq!(4, pow5_factor(42 * 5 * 5 * 5 * 5));  in test_pow5_factor()
67     assert_eq!(5, pow5_factor(42 * 5 * 5 * 5 * 5 * 5));  in test_pow5_factor()
69     assert_eq!(27, pow5_factor(7450580596923828125)); // 5^27, largest power of 5 < 2^64.  in test_pow5_factor()
70     assert_eq!(1, pow5_factor(18446744073709551615)); // 2^64 - 1, largest multiple of 5 < 2^64.  in test_pow5_factor()
71     assert_eq!(0, pow5_factor(18446744073709551614)); // 2^64 - 2, largest non-multiple of 5 < 2^64.  in test_pow5_factor()