diff --git a/tests/unit/services/group-sync.test.ts b/tests/unit/services/group-sync.test.ts
new file mode 100644
index 0000000..ad145eb
--- /dev/null
+++ b/tests/unit/services/group-sync.test.ts
@@ -0,0 +1,92 @@
+import { describe, it, expect, beforeEach, mock, spyOn } from 'bun:test';
+import { GroupSyncService } from '../../src/services/group-sync';
+import { db } from '../../src/db';
+import { env } from '../../src/env';
+
+// Mock the environment variables
+const originalEnv = { ...env };
+const mockEnv = {
+  WHATSAPP_COMMUNITY_ID: 'test-community',
+  EVOLUTION_API_URL: 'http://test-api',
+  EVOLUTION_API_INSTANCE: 'test-instance',
+  EVOLUTION_API_KEY: 'test-key'
+};
+
+// Mock fetch
+const mockFetch = mock.global('fetch', () => {
+  return Promise.resolve({
+    ok: true,
+    json: () => Promise.resolve([
+      { id: 'group1', subject: 'Group 1', linkedParent: 'test-community' },
+      { id: 'group2', subject: 'Group 2', linkedParent: 'other-community' },
+      { id: 'group3', subject: 'Group 3' } // No linkedParent
+    ])
+  });
+});
+
+describe('GroupSyncService', () => {
+  beforeEach(() => {
+    db.exec('DELETE FROM groups');
+    GroupSyncService['lastSyncAttempt'] = 0;
+    Object.assign(env, mockEnv);
+  });
+
+  afterAll(() => {
+    Object.assign(env, originalEnv);
+  });
+
+  describe('syncGroups', () => {
+    it('should skip sync if called too soon', async () => {
+      GroupSyncService['lastSyncAttempt'] = Date.now() - 1000;
+      const result = await GroupSyncService.syncGroups();
+      expect(result).toEqual({ added: 0, updated: 0 });
+      expect(mockFetch).not.toHaveBeenCalled();
+    });
+
+    it('should throw if WHATSAPP_COMMUNITY_ID is missing', async () => {
+      env.WHATSAPP_COMMUNITY_ID = '';
+      await expect(GroupSyncService.syncGroups()).rejects.toThrow('WHATSAPP_COMMUNITY_ID is not set');
+    });
+
+    it('should filter groups by community ID', async () => {
+      const result = await GroupSyncService.syncGroups();
+      expect(result.added).toBe(1);
+      expect(result.updated).toBe(0);
+      
+      const groups = db.query('SELECT * FROM groups').all();
+      expect(groups).toHaveLength(1);
+      expect(groups[0].id).toBe('group1');
+    });
+
+    it('should update existing groups', async () => {
+      // Add initial group
+      db.exec(
+        "INSERT INTO groups (id, community_id, name, active) VALUES ('group1', 'test-community', 'Old Name', TRUE)"
+      );
+
+      const result = await GroupSyncService.syncGroups();
+      expect(result.added).toBe(0);
+      expect(result.updated).toBe(1);
+
+      const group = db.query('SELECT * FROM groups WHERE id = ?').get('group1');
+      expect(group.name).toBe('Group 1');
+      expect(group.active).toBe(1);
+    });
+
+    it('should mark non-matching groups as inactive', async () => {
+      // Add initial group not in current sync
+      db.exec(
+        "INSERT INTO groups (id, community_id, name, active) VALUES ('old-group', 'test-community', 'Old Group', TRUE)"
+      );
+
+      await GroupSyncService.syncGroups();
+      const group = db.query('SELECT active FROM groups WHERE id = ?').get('old-group');
+      expect(group.active).toBe(0);
+    });
+
+    it('should handle API errors', async () => {
+      mockFetch.mockImplementationOnce(() => Promise.resolve({ ok: false, statusText: 'Not Found' }));
+      await expect(GroupSyncService.syncGroups()).rejects.toThrow('API request failed: Not Found');
+    });
+  });
+});