code: def test_fsdp_precision_forward_context():
      """Test to ensure that the context manager correctly is set to bfloat16."""
      precision = FSDPPrecision(precision="16-mixed")
      assert isinstance(precision.scaler, torch.cuda.amp.GradScaler)
      assert torch.get_default_dtype() == torch.float32
      with precision.forward_context():
          assert torch.get_autocast_gpu_dtype() == torch.float16
      assert isinstance(precision.forward_context(), torch.autocast)
      assert precision.forward_context().fast_dtype == torch.float16
  
      precision = FSDPPrecision(precision="16-true")
      assert precision.scaler is None
      assert torch.get_default_dtype() == torch.float32
      with precision.forward_context():
          assert torch.get_default_dtype() == torch.float16
      assert isinstance(
          precision.forward_context(), _DtypeContextManager
      )
      assert precision.forward_context()._new_dtype == torch.float16
  
      precision = FSDPPrecision(precision="bf16-mixed")
      assert precision.scaler is None
      with precision.forward_context():
          assert torch.get_autocast_gpu_dtype() == torch.bfloat16
      assert isinstance(precision.forward_context(), torch.autocast)
      assert precision.forward_context().fast_dtype == torch.bfloat16
  
      precision = FSDPPrecision(precision="bf16-true")
      assert precision.scaler is None
      with precision.forward_context():  # forward context is not using autocast ctx manager
          assert torch.get_default_dtype() == torch.bfloat16
      assert isinstance(
          precision.forward_context(), _DtypeContextManager
      )
      assert precision.forward_context()._new_dtype == torch.bfloat16
  
file_path: pytorch-lightning/tests/tests_pytorch/plugins/precision/test_fsdp.py
imports: from unittest.mock import ANY, MagicMock, Mock
  import pytest
  import torch
  from lightning.fabric.plugins.precision.utils import _DtypeContextManager
  from lightning.pytorch.plugins.precision.fsdp import FSDPPrecision
  from tests_pytorch.helpers.runif import RunIf
label_desc: Use image node_id 4 for calling a global function with example usage: test_fsdp_precision_forward_context() without return types