Add unit tests for FridayOfWeek date calculation

models_test.go

@@ -21,3 +21,115 @@ func TestReportWeekRangeMondayCutoff(t *testing.T) {
 		t.Fatalf("expected current week for Monday afternoon, got %s -> %s", from.Format("20060102"), to.Format("20060102"))
 	}
 }
+
+func TestFridayOfWeek(t *testing.T) {
+	loc := time.FixedZone("UTC+0", 0)
+
+	tests := []struct {
+		name     string
+		monday   time.Time
+		expected string
+	}{
+		{
+			name:     "basic monday to friday",
+			monday:   time.Date(2026, 2, 9, 0, 0, 0, 0, loc),
+			expected: "20260213", // Feb 13, 2026 (Friday)
+		},
+		{
+			name:     "monday with time component",
+			monday:   time.Date(2026, 2, 9, 14, 30, 45, 0, loc),
+			expected: "20260213", // Feb 13, 2026 (Friday)
+		},
+		{
+			name:     "year boundary - monday in december",
+			monday:   time.Date(2025, 12, 29, 0, 0, 0, 0, loc),
+			expected: "20260102", // Jan 2, 2026 (Friday)
+		},
+		{
+			name:     "year boundary - monday in january",
+			monday:   time.Date(2026, 1, 5, 0, 0, 0, 0, loc),
+			expected: "20260109", // Jan 9, 2026 (Friday)
+		},
+		{
+			name:     "month boundary",
+			monday:   time.Date(2026, 2, 23, 0, 0, 0, 0, loc),
+			expected: "20260227", // Feb 27, 2026 (Friday)
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			friday := FridayOfWeek(tt.monday)
+			got := friday.Format("20060102")
+			if got != tt.expected {
+				t.Errorf("FridayOfWeek(%s) = %s, want %s",
+					tt.monday.Format("20060102 15:04:05"), got, tt.expected)
+			}
+
+			// Verify it's actually a Friday
+			if friday.Weekday() != time.Friday {
+				t.Errorf("FridayOfWeek(%s) returned %s (weekday: %s), expected Friday",
+					tt.monday.Format("20060102"), friday.Format("20060102"), friday.Weekday())
+			}
+
+			// Verify time components are preserved
+			if friday.Hour() != tt.monday.Hour() || friday.Minute() != tt.monday.Minute() || friday.Second() != tt.monday.Second() {
+				t.Errorf("FridayOfWeek(%s) time component not preserved: got %02d:%02d:%02d, want %02d:%02d:%02d",
+					tt.monday.Format("20060102 15:04:05"),
+					friday.Hour(), friday.Minute(), friday.Second(),
+					tt.monday.Hour(), tt.monday.Minute(), tt.monday.Second())
+			}
+
+			// Verify location is preserved
+			if friday.Location() != tt.monday.Location() {
+				t.Errorf("FridayOfWeek(%s) location not preserved: got %v, want %v",
+					tt.monday.Format("20060102"), friday.Location(), tt.monday.Location())
+			}
+		})
+	}
+}
+
+func TestFridayOfWeekWithDifferentTimezones(t *testing.T) {
+	utc := time.UTC
+	pst := time.FixedZone("PST", -8*3600)
+	jst := time.FixedZone("JST", 9*3600)
+
+	tests := []struct {
+		name     string
+		monday   time.Time
+		expected string
+	}{
+		{
+			name:     "UTC timezone",
+			monday:   time.Date(2026, 2, 9, 10, 0, 0, 0, utc),
+			expected: "20260213",
+		},
+		{
+			name:     "PST timezone",
+			monday:   time.Date(2026, 2, 9, 10, 0, 0, 0, pst),
+			expected: "20260213",
+		},
+		{
+			name:     "JST timezone",
+			monday:   time.Date(2026, 2, 9, 10, 0, 0, 0, jst),
+			expected: "20260213",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			friday := FridayOfWeek(tt.monday)
+			got := friday.Format("20060102")
+			if got != tt.expected {
+				t.Errorf("FridayOfWeek(%s) = %s, want %s",
+					tt.monday.Format("20060102 15:04:05 MST"), got, tt.expected)
+			}
+
+			// Verify location is preserved
+			if friday.Location() != tt.monday.Location() {
+				t.Errorf("FridayOfWeek(%s) location not preserved: got %v, want %v",
+					tt.monday.Format("20060102 15:04:05 MST"), friday.Location(), tt.monday.Location())
+			}
+		})
+	}
+}