diff --git a/tests/helpers/db.ts b/tests/helpers/db.ts
new file mode 100644
index 0000000..a10b2ee
--- /dev/null
+++ b/tests/helpers/db.ts
@@ -0,0 +1,49 @@
+import Database, { type Database as SqliteDatabase } from 'bun:sqlite';
+import { initializeDatabase } from '../../src/db';
+
+// Servicios opcionales para inyección de DB en tests.
+// Importamos con nombres existentes en la base de código para respetar convenciones.
+import { TaskService } from '../../src/tasks/service';
+import { CommandService } from '../../src/services/command';
+import { ResponseQueue } from '../../src/services/response-queue';
+import { IdentityService } from '../../src/services/identity';
+import { GroupSyncService } from '../../src/services/group-sync';
+import { RemindersService } from '../../src/services/reminders';
+
+/**
+ * Crea una DB en memoria y aplica initializeDatabase() con todas las migraciones.
+ */
+export function makeMemDb(): SqliteDatabase {
+  const memdb = new Database(':memory:');
+  initializeDatabase(memdb);
+  return memdb;
+}
+
+/**
+ * Inyecta la instancia de DB en los servicios que la exponen como propiedad estática.
+ * Pensado para usarse en beforeAll/beforeEach de tests que usan estos servicios.
+ */
+export function injectAllServices(db: SqliteDatabase): void {
+  try { (TaskService as any).dbInstance = db; } catch {}
+  try { (CommandService as any).dbInstance = db; } catch {}
+  try { (ResponseQueue as any).dbInstance = db; } catch {}
+  try { (IdentityService as any).dbInstance = db; } catch {}
+  try { (GroupSyncService as any).dbInstance = db; } catch {}
+  try { (RemindersService as any).dbInstance = db; } catch {}
+}
+
+/**
+ * Restablece estado global/cachés en servicios entre tests.
+ * Best-effort: solo llama si existen los métodos.
+ */
+export function resetServices(): void {
+  try { (IdentityService as any).clearCache?.(); } catch {}
+  try { (GroupSyncService as any).clearCaches?.(); } catch {}
+  try { (CommandService as any).resetForTests?.(); } catch {}
+  try { (ResponseQueue as any).resetForTests?.(); } catch {}
+  try { (RemindersService as any).resetForTests?.(); } catch {}
+}
+
+/**
+ * Nota: en Etapa 1 añadiremos seedAllowed() aquí cuando exista AllowedGroups.
+ */
diff --git a/tests/setup.ts b/tests/setup.ts
new file mode 100644
index 0000000..8571b57
--- /dev/null
+++ b/tests/setup.ts
@@ -0,0 +1,7 @@
+/**
+ * Setup opcional para tests. Si el runner lo soporta (p. ej., bun test con --preload),
+ * fija el modo de gating por defecto a 'off' para no afectar suites existentes.
+ */
+if (!process.env.GROUP_GATING_MODE) {
+  process.env.GROUP_GATING_MODE = 'off';
+}
diff --git a/tests/unit/db/migrations.smoke.test.ts b/tests/unit/db/migrations.smoke.test.ts
new file mode 100644
index 0000000..28096fa
--- /dev/null
+++ b/tests/unit/db/migrations.smoke.test.ts
@@ -0,0 +1,18 @@
+import { describe, it, expect } from 'bun:test';
+import Database from 'bun:sqlite';
+import { initializeDatabase } from '../../../src/db';
+
+describe('DB migrations smoke', () => {
+  it('initializeDatabase en :memory: no lanza y crea tablas base', () => {
+    const memdb = new Database(':memory:');
+    expect(() => initializeDatabase(memdb)).not.toThrow();
+
+    // Comprobar que al menos una tabla base existe (users, tasks o response_queue).
+    const rows = memdb
+      .query(`SELECT name FROM sqlite_master WHERE type='table' AND name IN ('users','tasks','response_queue')`)
+      .all() as Array<{ name: string }>;
+
+    expect(Array.isArray(rows)).toBe(true);
+    expect(rows.length).toBeGreaterThan(0);
+  });
+});