Fix tests on single-GPU machine (#16911)

(cherry picked from commit 888686e)

Author: carmocca

tests/tests_fabric/plugins/precision/test_native_amp_integration.py

@@ -63,8 +63,8 @@ def after_backward(self, model):
     [
         ("cpu", 16, torch.bfloat16),
         ("cpu", "bf16", torch.bfloat16),
-        pytest.param("cuda", 16, torch.float16, marks=RunIf(min_cuda_gpus=1)),
-        pytest.param("cuda", "bf16", torch.bfloat16, marks=RunIf(min_cuda_gpus=1, bf16_cuda=True)),
+        pytest.param("cuda", 16, torch.float16, marks=RunIf(min_cuda_gpus=2)),
+        pytest.param("cuda", "bf16", torch.bfloat16, marks=RunIf(min_cuda_gpus=2, bf16_cuda=True)),
     ],
 )
 def test_native_mixed_precision(accelerator, precision, expected_dtype):

tests/tests_fabric/test_connector.py

@@ -380,7 +380,7 @@ def test_set_devices_if_none_cpu():
 @RunIf(mps=False)
 def test_unsupported_strategy_types_on_cpu_and_fallback():
     with pytest.warns(UserWarning, match="is not supported on CPUs, hence setting `strategy='ddp"):
-        connector = _Connector(strategy="dp", devices=2)
+        connector = _Connector(accelerator="cpu", strategy="dp", devices=2)
     assert isinstance(connector.strategy, DDPStrategy)
 
 
@@ -462,9 +462,9 @@ def test_strategy_choice_ddp_spawn_cpu():
 @RunIf(skip_windows=True)
 @mock.patch("lightning_fabric.connector._IS_INTERACTIVE", True)
 def test_strategy_choice_ddp_fork_in_interactive():
-    """Test that when accelerator and strategy are unspecified, the connector chooses DDP Fork in interactive
-    environments by default."""
-    connector = _Connector(devices=2)
+    """Test that when strategy is unspecified, the connector chooses DDP Fork in interactive environments by
+    default."""
+    connector = _Connector(accelerator="cpu", devices=2)
     assert isinstance(connector.accelerator, CPUAccelerator)
     assert isinstance(connector.strategy, DDPStrategy)
     assert isinstance(connector.strategy.cluster_environment, LightningEnvironment)
@@ -766,7 +766,7 @@ def test_precision_selection_16_on_cpu_warns():
     with pytest.warns(
         UserWarning, match=r"precision=16\)` but native AMP is not supported on CPU. Using `precision='bf16"
     ):
-        _Connector(precision=16)
+        _Connector(accelerator="cpu", precision=16)
 
 
 class MyNativeAMP(MixedPrecision):
@@ -784,6 +784,7 @@ def test_precision_selection_amp_ddp(strategy, devices, is_custom_plugin, plugin
     if is_custom_plugin:
         plugin = plugin_cls(16, "cpu")
     connector = _Connector(
+        accelerator="cpu",
         precision=16,
         devices=devices,
         strategy=strategy,
@@ -833,7 +834,7 @@ def test_accelerator_strategy_from_environment(accelerator, strategy, expected_a
         env_vars["LT_STRATEGY"] = strategy
 
     with mock.patch.dict(os.environ, env_vars):
-        connector = _Connector()
+        connector = _Connector(accelerator="cpu" if accelerator is None else "auto")
         assert isinstance(connector.accelerator, expected_accelerator)
         assert isinstance(connector.strategy, expected_strategy)
 
@@ -877,7 +878,7 @@ def test_arguments_from_environment_collision():
 def test_fsdp_unsupported_on_cpu(_):
     """Test that we raise an error if attempting to run FSDP without GPU."""
     with pytest.raises(ValueError, match="You selected the FSDP strategy but FSDP is only available on GPU"):
-        _Connector(strategy="fsdp")
+        _Connector(accelerator="cpu", strategy="fsdp")
 
 
 def test_connector_defaults_match_fabric_defaults():

tests/tests_pytorch/trainer/connectors/test_accelerator_connector.py

@@ -514,9 +514,9 @@ def test_strategy_choice_ddp_spawn_cpu():
 @RunIf(skip_windows=True)
 @mock.patch("pytorch_lightning.trainer.connectors.accelerator_connector._IS_INTERACTIVE", True)
 def test_strategy_choice_ddp_fork_in_interactive():
-    """Test that when accelerator and strategy are unspecified, the connector chooses DDP Fork in interactive
-    environments by default."""
-    trainer = Trainer(devices=2)
+    """Test that when strategy is unspecified, the connector chooses DDP Fork in interactive environments by
+    default."""
+    trainer = Trainer(accelerator="cpu", devices=2)
     assert isinstance(trainer.accelerator, CPUAccelerator)
     assert isinstance(trainer.strategy, DDPSpawnStrategy)
     assert isinstance(trainer.strategy.cluster_environment, LightningEnvironment)