luhn_test.gno

 1package luhn
 2
 3import (
 4	"strings"
 5	"testing"
 6
 7	"gno.land/p/nt/uassert/v0"
 8)
 9
10func TestValid(t *testing.T) {
11	cases := []struct {
12		name string
13		in   string
14		want bool
15	}{
16		{"known-good test card", "4539148803436467", true},
17		{"spaces ignored", "4539 1488 0343 6467", true},
18		{"hyphens ignored", "4539-1488-0343-6467", true},
19		{"single digit flipped", "4539148803436468", false},
20		{"adjacent transposition", "4539148803436647", false},
21		{"classic 79927398713", "79927398713", true},
22		{"classic off by one", "79927398710", false},
23		{"all zeros is valid", "00", true},
24		{"letters rejected", "4539abc8803436467", false},
25		{"empty rejected", "", false},
26		{"one digit rejected", "7", false},
27		{"separators only rejected", " - ", false},
28		{"over MaxLen rejected", strings.Repeat("0", MaxLen+1), false},
29	}
30	for _, c := range cases {
31		t.Run(c.name, func(t *testing.T) {
32			uassert.Equal(t, c.want, Valid(c.in))
33		})
34	}
35}
36
37func TestCheckDigit(t *testing.T) {
38	cases := []struct {
39		payload string
40		want    int
41	}{
42		{"7992739871", 3},
43		{"453914880343646", 7},
44		{"0", 0},
45	}
46	for _, c := range cases {
47		got, ok := CheckDigit(c.payload)
48		uassert.True(t, ok)
49		uassert.Equal(t, c.want, got)
50	}
51}
52
53func TestCheckDigitRejectsBadInput(t *testing.T) {
54	for _, in := range []string{"", "abc", " - "} {
55		_, ok := CheckDigit(in)
56		uassert.False(t, ok)
57	}
58}
59
60// Append must produce something Valid accepts — the round-trip property.
61func TestAppendRoundTrip(t *testing.T) {
62	payloads := []string{"7992739871", "453914880343646", "1", "123456789012345"}
63	for _, p := range payloads {
64		got, ok := Append(p)
65		uassert.True(t, ok)
66		uassert.True(t, Valid(got))
67		uassert.Equal(t, len(p)+1, len(got))
68	}
69}
70
71// Append strips separators, so a spaced payload yields the same digits.
72func TestAppendStripsSeparators(t *testing.T) {
73	a, ok := Append("4539 1488 0343 646")
74	uassert.True(t, ok)
75	b, ok2 := Append("453914880343646")
76	uassert.True(t, ok2)
77	uassert.Equal(t, b, a)
78	uassert.Equal(t, "4539148803436467", a)
79}
80
81// Every single-digit change to a valid number must be caught: that is the
82// guarantee Luhn actually makes.
83func TestDetectsEverySingleDigitError(t *testing.T) {
84	const base = "4539148803436467"
85	uassert.True(t, Valid(base))
86	for i := 0; i < len(base); i++ {
87		for d := byte('0'); d <= '9'; d++ {
88			if d == base[i] {
89				continue
90			}
91			mutated := base[:i] + string(d) + base[i+1:]
92			uassert.False(t, Valid(mutated))
93		}
94	}
95}