code: def test_returns_backend_types(self):
      response = client.post("/api/backends/list_types")
      assert response.status_code == 200, response.json()
      assert response.json() == [
          "aws",
          "azure",
          "datacrunch",
          "gcp",
          "lambda",
          "nebius",
          "tensordock",
          "vastai",
      ]
  
imports: import json
  from unittest.mock import Mock, patch
  import pytest
  from fastapi.testclient import TestClient
  from sqlalchemy import select
  from sqlalchemy.ext.asyncio import AsyncSession
  from dstack._internal.core.errors import BackendAuthError
  from dstack._internal.core.models.users import GlobalRole, ProjectRole
  from dstack._internal.server.main import app
  from dstack._internal.server.models import BackendModel
  from dstack._internal.server.services.projects import add_project_member
  from dstack._internal.server.testing.common import create_backend, create_project, create_user, get_auth_headers
label_desc: Use image node_id 1 for calling the TestListBackendTypes obj's underlying member method code with example usage: obj.test_returns_backend_types() without return types