diff --git a/src/services/group-sync.ts b/src/services/group-sync.ts
index ebfb045..834434d 100644
--- a/src/services/group-sync.ts
+++ b/src/services/group-sync.ts
@@ -33,6 +33,9 @@ type EvolutionGroup = {
 };
 
 export class GroupSyncService {
+	// Static property for DB instance injection (defaults to global db)
+	static dbInstance: Database = db;
+
 	/**
 	 * Gets the sync interval duration in milliseconds.
 	 * 
@@ -92,12 +95,12 @@ export class GroupSyncService {
 				parent: g.linkedParent
 			})));
 
-			const dbGroupsBefore = db.prepare('SELECT id, active FROM groups').all();
+			const dbGroupsBefore = this.dbInstance.prepare('SELECT id, active FROM groups').all();
 			console.log('ℹ️ Grupos en DB antes de upsert:', dbGroupsBefore);
 
 			const result = await this.upsertGroups(communityGroups);
 			
-			const dbGroupsAfter = db.prepare('SELECT id, active FROM groups').all();
+			const dbGroupsAfter = this.dbInstance.prepare('SELECT id, active FROM groups').all();
 			console.log('ℹ️ Grupos en DB después de upsert:', dbGroupsAfter);
 
 			return result;
@@ -187,7 +190,7 @@ export class GroupSyncService {
 			return groups;
 		} catch (error) {
 			console.error('❌ Failed to fetch groups:', {
-				error: error instanceof Error ? error.message : String(error),
+				error: error instanceof Error ? error.message : String(e),
 				stack: error instanceof Error ? error.stack : undefined
 			});
 			throw error;
@@ -195,7 +198,7 @@ export class GroupSyncService {
 	}
 
 	private static cacheActiveGroups(): void {
-		const groups = db.prepare('SELECT id, name FROM groups WHERE active = TRUE').all();
+		const groups = this.dbInstance.prepare('SELECT id, name FROM groups WHERE active = TRUE').all();
 		activeGroupsCache.clear();
 		for (const group of groups) {
 			activeGroupsCache.set(group.id, group.name);
@@ -204,7 +207,7 @@ export class GroupSyncService {
 	}
 
 	private static getActiveGroupsCount(): number {
-		const result = db.prepare('SELECT COUNT(*) as count FROM groups WHERE active = TRUE').get();
+		const result = this.dbInstance.prepare('SELECT COUNT(*) as count FROM groups WHERE active = TRUE').get();
 		return result?.count || 0;
 	}
 
@@ -275,9 +278,9 @@ export class GroupSyncService {
 		let added = 0;
 		let updated = 0;
 
-		const transactionResult = db.transaction(() => {
+		const transactionResult = this.dbInstance.transaction(() => {
 			// First mark all groups as inactive and update verification timestamp
-			const inactiveResult = db.prepare(`
+			const inactiveResult = this.dbInstance.prepare(`
         UPDATE groups 
         SET active = FALSE, 
             last_verified = CURRENT_TIMESTAMP
@@ -289,17 +292,17 @@ export class GroupSyncService {
 			});
 
 			for (const group of groups) {
-				const existing = db.prepare('SELECT 1 FROM groups WHERE id = ?').get(group.id);
+				const existing = this.dbInstance.prepare('SELECT 1 FROM groups WHERE id = ?').get(group.id);
 				console.log('Checking group:', group.id, 'exists:', !!existing);
 
 				if (existing) {
-					const updateResult = db.prepare(
+					const updateResult = this.dbInstance.prepare(
 						'UPDATE groups SET name = ?, active = TRUE, last_verified = CURRENT_TIMESTAMP WHERE id = ?'
 					).run(group.subject, group.id);
 					console.log('Updated group:', group.id, 'result:', updateResult);
 					updated++;
 				} else {
-					const insertResult = db.prepare(
+					const insertResult = this.dbInstance.prepare(
 						'INSERT INTO groups (id, community_id, name, active) VALUES (?, ?, ?, TRUE)'
 					).run(group.id, env.WHATSAPP_COMMUNITY_ID, group.subject);
 					console.log('Added group:', group.id, 'result:', insertResult);
diff --git a/tests/unit/server.test.ts b/tests/unit/server.test.ts
index 242fb42..d974148 100644
--- a/tests/unit/server.test.ts
+++ b/tests/unit/server.test.ts
@@ -47,6 +47,9 @@ beforeEach(() => {
   // Inject testDb for WebhookServer to use
   WebhookServer.dbInstance = testDb;
   
+  // Inject testDb for GroupSyncService to use
+  GroupSyncService.dbInstance = testDb;
+  
   // Ensure database is initialized (recreates tables if dropped)
   initializeDatabase(testDb);
   
@@ -62,7 +65,7 @@ beforeEach(() => {
     VALUES ('group-id@g.us', 'test-community', 'Test Group', 1)
   `);
 
-  // Populate active groups cache
+  // Populate active groups cache with test data
   GroupSyncService['cacheActiveGroups']();
 });