test: add unit tests for SunCalc functionality

- Introduced comprehensive unit tests for the SunCalc package, covering the creation of SunCalc instances and retrieval of sun event times.
- Implemented tests for sunrise and sunset time retrieval, ensuring that the returned times are valid and not zero.
- Added cache consistency tests to verify that cached sun event times are correctly stored and retrieved.
- These tests enhance the reliability of the SunCalc functionality and ensure accurate calculations for given coordinates.

internal/suncalc/suncalc_test.go

@@ -0,0 +1,121 @@
+package suncalc
+
+import (
+	"testing"
+	"time"
+)
+
+func TestNewSunCalc(t *testing.T) {
+	latitude, longitude := 60.1699, 24.9384 // Helsinki coordinates
+	sc := NewSunCalc(latitude, longitude)
+	if sc == nil {
+		t.Fatal("NewSunCalc returned nil")
+	}
+
+	if sc.observer.Latitude != latitude {
+		t.Errorf("Expected latitude %v, got %v", latitude, sc.observer.Latitude)
+	}
+
+	if sc.observer.Longitude != longitude {
+		t.Errorf("Expected longitude %v, got %v", longitude, sc.observer.Longitude)
+	}
+}
+
+func TestGetSunEventTimes(t *testing.T) {
+	// Helsinki coordinates
+	sc := NewSunCalc(60.1699, 24.9384)
+
+	// Test date (midsummer in Helsinki)
+	date := time.Date(2024, 6, 21, 0, 0, 0, 0, time.UTC)
+
+	// First call to calculate and cache
+	times1, err := sc.GetSunEventTimes(date)
+	if err != nil {
+		t.Fatalf("Failed to get sun event times: %v", err)
+	}
+
+	// Verify times are not zero
+	if times1.Sunrise.IsZero() {
+		t.Error("Sunrise time is zero")
+	}
+	if times1.Sunset.IsZero() {
+		t.Error("Sunset time is zero")
+	}
+	if times1.CivilDawn.IsZero() {
+		t.Error("Civil dawn time is zero")
+	}
+	if times1.CivilDusk.IsZero() {
+		t.Error("Civil dusk time is zero")
+	}
+
+	// Second call to test cache
+	times2, err := sc.GetSunEventTimes(date)
+	if err != nil {
+		t.Fatalf("Failed to get cached sun event times: %v", err)
+	}
+
+	// Verify cached times match original times
+	if !times1.Sunrise.Equal(times2.Sunrise) {
+		t.Error("Cached sunrise time doesn't match original")
+	}
+	if !times1.Sunset.Equal(times2.Sunset) {
+		t.Error("Cached sunset time doesn't match original")
+	}
+}
+
+func TestGetSunriseTime(t *testing.T) {
+	sc := NewSunCalc(60.1699, 24.9384)
+	date := time.Date(2024, 6, 21, 0, 0, 0, 0, time.UTC)
+
+	sunrise, err := sc.GetSunriseTime(date)
+	if err != nil {
+		t.Fatalf("Failed to get sunrise time: %v", err)
+	}
+
+	if sunrise.IsZero() {
+		t.Error("Sunrise time is zero")
+	}
+}
+
+func TestGetSunsetTime(t *testing.T) {
+	sc := NewSunCalc(60.1699, 24.9384)
+	date := time.Date(2024, 6, 21, 0, 0, 0, 0, time.UTC)
+
+	sunset, err := sc.GetSunsetTime(date)
+	if err != nil {
+		t.Fatalf("Failed to get sunset time: %v", err)
+	}
+
+	if sunset.IsZero() {
+		t.Error("Sunset time is zero")
+	}
+}
+
+func TestCacheConsistency(t *testing.T) {
+	sc := NewSunCalc(60.1699, 24.9384)
+	date := time.Date(2024, 6, 21, 0, 0, 0, 0, time.UTC)
+
+	// Get times twice
+	times1, err := sc.GetSunEventTimes(date)
+	if err != nil {
+		t.Fatalf("Failed to get initial sun event times: %v", err)
+	}
+
+	// Verify cache entry exists
+	dateKey := date.Format("2006-01-02")
+	sc.lock.RLock()
+	entry, exists := sc.cache[dateKey]
+	sc.lock.RUnlock()
+
+	if !exists {
+		t.Error("Cache entry not found after calculation")
+	}
+
+	if !entry.date.Equal(date) {
+		t.Error("Cached date doesn't match requested date")
+	}
+
+	if !entry.times.Sunrise.Equal(times1.Sunrise) {
+		t.Error("Cached sunrise time doesn't match calculated time")
+	}
+}