lightning/tests/tests_fabric/strategies/test_single_device.py

# Copyright The PyTorch Lightning team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from unittest.mock import Mock

import pytest
import torch

from lightning_fabric.strategies import SingleDeviceStrategy


def test_single_device_default_device():
    assert SingleDeviceStrategy().root_device == torch.device("cpu")


@pytest.mark.parametrize("device", ["cpu", torch.device("cpu"), "cuda:1", torch.device("cuda")])
def test_single_device_root_device(device):
    assert SingleDeviceStrategy(device).root_device == torch.device(device)


@pytest.mark.parametrize("device", [torch.device("cpu"), torch.device("cuda", 3)])
def test_single_device_ranks(device):
    strategy = SingleDeviceStrategy(device)
    assert strategy.world_size == 1
    assert strategy.local_rank == 0
    assert strategy.global_rank == 0
    assert strategy.is_global_zero


def test_single_device_collectives():
    """Test that collectives in the single-device strategy act as the identity."""
    strategy = SingleDeviceStrategy()
    tensor = Mock()
    assert strategy.all_gather(tensor) == tensor
    assert strategy.all_reduce(tensor) == tensor
    assert strategy.broadcast(tensor) == tensor


def test_single_device_module_to_device():
    strategy = SingleDeviceStrategy()
    strategy._root_device = Mock()
    module = Mock(spec=torch.nn.Module)
    strategy.module_to_device(module)
    module.to.assert_called_with(strategy.root_device)