fraction_test.gno

 1package fraction
 2
 3import (
 4	"testing"
 5
 6	"gno.land/p/nt/uassert/v0"
 7)
 8
 9func mk(t *testing.T, n, d int64) Fraction {
10	t.Helper()
11	f, err := New(n, d)
12	uassert.NoError(t, err)
13	return f
14}
15
16func TestNewReduces(t *testing.T) {
17	uassert.Equal(t, "1/2", mk(t, 2, 4).String())
18	uassert.Equal(t, "2", mk(t, 6, 3).String())
19	uassert.Equal(t, "0", mk(t, 0, 5).String())
20}
21
22// The sign always lives in the numerator, so -1/2 and 1/-2 are the same value.
23func TestSignNormalised(t *testing.T) {
24	a := mk(t, 1, -2)
25	uassert.Equal(t, "-1/2", a.String())
26	uassert.True(t, a.Equal(mk(t, -1, 2)))
27	uassert.True(t, mk(t, -2, -4).Equal(mk(t, 1, 2)))
28}
29
30func TestZeroDenominator(t *testing.T) {
31	_, err := New(1, 0)
32	uassert.ErrorIs(t, err, ErrZeroDenominator)
33}
34
35// The headline: exact arithmetic where floats would drift.
36func TestExactThirds(t *testing.T) {
37	third := mk(t, 1, 3)
38	sum, ok := third.Add(third)
39	uassert.True(t, ok)
40	sum, ok = sum.Add(third)
41	uassert.True(t, ok)
42	uassert.Equal(t, "1", sum.String()) // exactly 1, not 0.9999…
43}
44
45func TestArithmetic(t *testing.T) {
46	a, b := mk(t, 1, 2), mk(t, 1, 3)
47	s, _ := a.Add(b)
48	uassert.Equal(t, "5/6", s.String())
49	d, _ := a.Sub(b)
50	uassert.Equal(t, "1/6", d.String())
51	m, _ := a.Mul(b)
52	uassert.Equal(t, "1/6", m.String())
53	q, _ := a.Div(b)
54	uassert.Equal(t, "3/2", q.String())
55	uassert.Equal(t, "-1/2", a.Neg().String())
56}
57
58func TestDivByZero(t *testing.T) {
59	_, ok := mk(t, 1, 2).Div(Zero())
60	uassert.False(t, ok)
61}
62
63// Overflow must be reported, never silently wrapped into a wrong answer.
64func TestOverflowReported(t *testing.T) {
65	big := Fraction{num: 1 << 62, den: 3}
66	_, ok := big.Mul(Fraction{num: 1 << 62, den: 5})
67	uassert.False(t, ok)
68	_, ok2 := big.Add(Fraction{num: 1 << 62, den: 7})
69	uassert.False(t, ok2)
70}
71
72// Comparison is exact: cross-multiplication, never a decimal detour.
73func TestCmp(t *testing.T) {
74	uassert.Equal(t, -1, mk(t, 1, 3).Cmp(mk(t, 1, 2)))
75	uassert.Equal(t, 1, mk(t, 2, 3).Cmp(mk(t, 1, 2)))
76	uassert.Equal(t, 0, mk(t, 2, 4).Cmp(mk(t, 1, 2)))
77	// 1/3 vs 33333/100000 — a decimal comparison at 5 places would call these equal
78	uassert.Equal(t, 1, mk(t, 1, 3).Cmp(mk(t, 33333, 100000)))
79}
80
81func TestDecimal(t *testing.T) {
82	uassert.Equal(t, "0.333", Decimal(mk(t, 1, 3), 3))
83	uassert.Equal(t, "0.5", Decimal(mk(t, 1, 2), 1))
84	uassert.Equal(t, "1", Decimal(mk(t, 3, 2), 0)) // truncates toward zero
85	uassert.Equal(t, "-0.333", Decimal(mk(t, -1, 3), 3))
86	uassert.Equal(t, "2.000", Decimal(Int(2), 3))
87	uassert.Equal(t, "0", Decimal(Zero(), 0))
88}
89
90// The zero value must behave as 0/1 rather than dividing by zero.
91func TestZeroValueUsable(t *testing.T) {
92	var f Fraction
93	uassert.Equal(t, int64(1), f.Den())
94	uassert.True(t, f.IsZero())
95	uassert.Equal(t, "0", f.String())
96	s, ok := f.Add(Int(1))
97	uassert.True(t, ok)
98	uassert.Equal(t, "1", s.String())
99}