test(schedule): cover dst transition logic

utils/__tests__/schedule.test.ts

@@ -99,6 +99,74 @@ describe('Schedule Utilities', () => {
       const schedule = generateSchedule([medication], baseDate);
       expect(schedule).toEqual([]);
     });
+
+    describe('DST boundaries', () => {
+      test('maintains morning doses during spring forward transition', () => {
+        const medication = createMockMedication({
+          frequency: Frequency.Daily,
+          startTime: '08:00',
+        });
+
+        const beforeTransition = generateSchedule(
+          [medication],
+          new Date('2024-03-09T12:00:00.000Z')
+        );
+        const duringTransition = generateSchedule(
+          [medication],
+          new Date('2024-03-10T12:00:00.000Z')
+        );
+
+        expect(beforeTransition).toHaveLength(1);
+        expect(duringTransition).toHaveLength(1);
+        const diffHours =
+          (duringTransition[0].scheduledTime.getTime() -
+            beforeTransition[0].scheduledTime.getTime()) /
+          3600000;
+        expect(diffHours).toBe(23);
+      });
+
+      test('shifts to next valid slot when scheduled time is skipped by DST', () => {
+        const medication = createMockMedication({
+          frequency: Frequency.Daily,
+          startTime: '02:30',
+        });
+
+        const schedule = generateSchedule(
+          [medication],
+          new Date('2024-03-10T12:00:00.000Z')
+        );
+
+        expect(schedule).toHaveLength(1);
+        expect(schedule[0].scheduledTime.getHours()).toBe(3);
+        expect(schedule[0].scheduledTime.getMinutes()).toBe(30);
+      });
+
+      test('extends interval by one hour during fall back transition', () => {
+        const medication = createMockMedication({
+          frequency: Frequency.Daily,
+          startTime: '08:00',
+        });
+
+        const beforeTransition = generateSchedule(
+          [medication],
+          new Date('2024-11-02T12:00:00.000Z')
+        );
+        const duringTransition = generateSchedule(
+          [medication],
+          new Date('2024-11-03T12:00:00.000Z')
+        );
+
+        expect(beforeTransition).toHaveLength(1);
+        expect(duringTransition).toHaveLength(1);
+        const diffHours =
+          (duringTransition[0].scheduledTime.getTime() -
+            beforeTransition[0].scheduledTime.getTime()) /
+          3600000;
+        expect(diffHours).toBe(25);
+        expect(duringTransition[0].scheduledTime.getHours()).toBe(8);
+        expect(duringTransition[0].scheduledTime.getMinutes()).toBe(0);
+      });
+    });
   });
 
   describe('generateReminderSchedule', () => {