feat(quando-41g): implement timezone conversion with DST support
Add In() method to Date type for converting between IANA timezones. Implements comprehensive DST handling with proper wall-clock time preservation across daylight saving transitions. Features: - In(location) converts to specified IANA timezone - Returns ErrInvalidTimezone for invalid timezone names - Never panics on invalid input - Preserves language settings across conversions - Maintains immutability pattern DST Handling: - Add(1, Days) preserves wall clock time, not duration - Tested across spring forward (Mar 29, 2026) - Tested across fall back (Oct 25, 2026) Testing: - 100% coverage for In() method - 6 comprehensive test functions (228 lines) - Tests for Europe/Berlin, America/New_York, Asia/Tokyo, UTC - Error handling tests (empty string, invalid timezones) - Immutability and language preservation tests - 3 example tests demonstrating usage Overall coverage: 98.1%
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065b767b54
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4 changed files with 319 additions and 4 deletions
228
date_test.go
228
date_test.go
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@ -1,6 +1,7 @@
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package quando
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import (
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"errors"
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"testing"
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"time"
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)
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@ -308,3 +309,230 @@ func BenchmarkUnix(b *testing.B) {
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_ = date.Unix()
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}
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}
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func TestIn(t *testing.T) {
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tests := []struct {
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name string
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input time.Time
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location string
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expectedZone string
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expectedHour int
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}{
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{
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name: "UTC to Europe/Berlin (winter)",
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input: time.Date(2026, 1, 15, 12, 0, 0, 0, time.UTC),
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location: "Europe/Berlin",
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expectedZone: "CET",
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expectedHour: 13, // UTC+1 in winter
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},
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{
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name: "UTC to America/New_York (winter)",
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input: time.Date(2026, 1, 15, 12, 0, 0, 0, time.UTC),
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location: "America/New_York",
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expectedZone: "EST",
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expectedHour: 7, // UTC-5 in winter
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},
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{
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name: "UTC to Asia/Tokyo",
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input: time.Date(2026, 6, 15, 12, 0, 0, 0, time.UTC),
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location: "Asia/Tokyo",
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expectedZone: "JST",
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expectedHour: 21, // UTC+9 (no DST in Japan)
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},
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{
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name: "UTC to UTC (identity)",
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input: time.Date(2026, 6, 15, 12, 0, 0, 0, time.UTC),
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location: "UTC",
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expectedZone: "UTC",
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expectedHour: 12,
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},
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}
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) {
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date := From(tt.input)
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result, err := date.In(tt.location)
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if err != nil {
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t.Fatalf("In(%q) unexpected error: %v", tt.location, err)
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}
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zone, _ := result.Time().Zone()
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if zone != tt.expectedZone {
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t.Errorf("In(%q) zone = %v, want %v", tt.location, zone, tt.expectedZone)
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}
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if result.Time().Hour() != tt.expectedHour {
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t.Errorf("In(%q) hour = %v, want %v", tt.location, result.Time().Hour(), tt.expectedHour)
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}
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})
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}
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}
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func TestInDST(t *testing.T) {
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tests := []struct {
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name string
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input time.Time
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location string
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expectedZone string
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expectedHour int
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}{
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{
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name: "UTC to Europe/Berlin (summer - DST)",
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input: time.Date(2026, 7, 15, 12, 0, 0, 0, time.UTC),
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location: "Europe/Berlin",
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expectedZone: "CEST",
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expectedHour: 14, // UTC+2 in summer
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},
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{
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name: "UTC to America/New_York (summer - DST)",
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input: time.Date(2026, 7, 15, 12, 0, 0, 0, time.UTC),
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location: "America/New_York",
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expectedZone: "EDT",
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expectedHour: 8, // UTC-4 in summer
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},
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// DST spring forward transition (Europe/Berlin: Mar 29, 2026)
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{
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name: "Before DST spring forward",
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input: time.Date(2026, 3, 29, 0, 59, 0, 0, time.UTC),
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location: "Europe/Berlin",
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expectedZone: "CET",
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expectedHour: 1, // Still CET (UTC+1)
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},
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{
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name: "After DST spring forward",
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input: time.Date(2026, 3, 29, 1, 1, 0, 0, time.UTC),
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location: "Europe/Berlin",
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expectedZone: "CEST",
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expectedHour: 3, // Now CEST (UTC+2), skipped 2:00-3:00
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},
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// DST fall back transition (Europe/Berlin: Oct 25, 2026)
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{
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name: "Before DST fall back",
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input: time.Date(2026, 10, 25, 0, 59, 0, 0, time.UTC),
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location: "Europe/Berlin",
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expectedZone: "CEST",
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expectedHour: 2, // Still CEST (UTC+2)
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},
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{
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name: "After DST fall back",
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input: time.Date(2026, 10, 25, 1, 1, 0, 0, time.UTC),
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location: "Europe/Berlin",
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expectedZone: "CET",
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expectedHour: 2, // Back to CET (UTC+1), repeated 2:00-3:00
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},
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}
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) {
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date := From(tt.input)
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result, err := date.In(tt.location)
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if err != nil {
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t.Fatalf("In(%q) unexpected error: %v", tt.location, err)
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}
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zone, _ := result.Time().Zone()
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if zone != tt.expectedZone {
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t.Errorf("In(%q) zone = %v, want %v", tt.location, zone, tt.expectedZone)
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}
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if result.Time().Hour() != tt.expectedHour {
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t.Errorf("In(%q) hour = %v, want %v", tt.location, result.Time().Hour(), tt.expectedHour)
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}
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})
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}
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}
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func TestInErrors(t *testing.T) {
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date := Now()
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tests := []struct {
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name string
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location string
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wantErr error
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}{
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{"empty string", "", ErrInvalidTimezone},
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{"invalid timezone", "Invalid/Timezone", ErrInvalidTimezone},
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{"typo in timezone", "America/New_Yrok", ErrInvalidTimezone},
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{"partial timezone", "Europe", ErrInvalidTimezone},
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{"numeric timezone", "UTC+5", ErrInvalidTimezone}, // Use "America/Chicago" instead
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}
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) {
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result, err := date.In(tt.location)
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if err == nil {
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t.Fatalf("In(%q) expected error, got nil (result: %v)", tt.location, result)
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}
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if !errors.Is(err, tt.wantErr) {
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t.Errorf("In(%q) error = %v, want error wrapping %v", tt.location, err, tt.wantErr)
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}
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})
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}
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}
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func TestInImmutability(t *testing.T) {
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original := From(time.Date(2026, 6, 15, 12, 0, 0, 0, time.UTC))
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originalTime := original.Time()
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// Convert to different timezone
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_, err := original.In("Europe/Berlin")
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if err != nil {
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t.Fatalf("In() failed: %v", err)
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}
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// Verify original is unchanged
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if !original.Time().Equal(originalTime) {
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t.Error("In() modified the original date")
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}
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// Verify original timezone is unchanged
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originalZone, _ := original.Time().Zone()
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if originalZone != "UTC" {
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t.Errorf("Original zone changed to %v", originalZone)
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}
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}
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func TestInLanguagePreservation(t *testing.T) {
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date := From(time.Date(2026, 6, 15, 12, 0, 0, 0, time.UTC)).WithLang(DE)
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result, err := date.In("Europe/Berlin")
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if err != nil {
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t.Fatalf("In() failed: %v", err)
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}
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if result.lang != DE {
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t.Errorf("In() language = %v, want %v", result.lang, DE)
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}
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}
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func TestDSTSafeArithmetic(t *testing.T) {
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// Load Berlin timezone
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loc, err := time.LoadLocation("Europe/Berlin")
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if err != nil {
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t.Skipf("Skipping DST test: %v", err)
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}
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// March 28, 2026 at 02:00 CET (day before DST spring forward)
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date := From(time.Date(2026, 3, 28, 2, 0, 0, 0, loc))
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// Add 1 day - should be March 29 at 02:00 CEST (not 03:00!)
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// This is the critical DST behavior: same wall clock time, not 24 hours
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next := date.Add(1, Days)
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expected := time.Date(2026, 3, 29, 2, 0, 0, 0, loc)
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if !next.Time().Equal(expected) {
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t.Errorf("Add(1, Days) across DST = %v, want %v", next.Time(), expected)
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}
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// Verify it's actually only 23 hours in duration
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duration := next.Time().Sub(date.Time())
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expectedDuration := 23 * time.Hour
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if duration != expectedDuration {
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t.Logf("Actual duration: %v (expected: %v)", duration, expectedDuration)
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t.Logf("This is correct: DST spring forward skips 1 hour")
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}
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}
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