deprecation tests

Author: DuYicong515

CHANGELOG.md

@@ -561,6 +561,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Deprecated `Trainer.data_parallel_device_ids` in favor of `Trainer.device_ids` ([#12072](https://github.com/PyTorchLightning/pytorch-lightning/pull/12072))
 
 
+- Deprecated `Trainer.gpus` in favor of `Trainer.device_ids` or `Trainer.num_devices` ([#12436](https://github.com/PyTorchLightning/pytorch-lightning/pull/12436))
+
+
 ### Removed
 
 - Removed deprecated parameter `method` in `pytorch_lightning.utilities.model_helpers.is_overridden` ([#10507](https://github.com/PyTorchLightning/pytorch-lightning/pull/10507))

pytorch_lightning/callbacks/gpu_stats_monitor.py

@@ -128,8 +128,8 @@ def setup(self, trainer: "pl.Trainer", pl_module: "pl.LightningModule", stage: O
 
         if trainer.strategy.root_device.type != "cuda":
             raise MisconfigurationException(
-                "You are using GPUStatsMonitor but are not running on GPU"
-                f" since gpus attribute in Trainer is set to {trainer.gpus}."
+                "You are using GPUStatsMonitor but are not running on GPU."
+                f" The root device type is {trainer.strategy.root_device.type}."
             )
 
         # The logical device IDs for selected devices

tests/deprecated_api/test_remove_1-8.py

@@ -1054,3 +1054,24 @@ def test_trainer_data_parallel_device_ids(monkeypatch, trainer_kwargs, expected_
         " Please use `Trainer.device_ids` instead."
     ):
         assert trainer.data_parallel_device_ids == expected_data_parallel_device_ids
+
+
+@pytest.mark.parametrize(
+    "trainer_kwargs",
+    [
+        {"accelerator": "gpu", "devices": 2},
+        {"accelerator": "gpu", "devices": [0, 2]},
+        {"accelerator": "gpu", "devices": "0"},
+        {"accelerator": "gpu", "devices": "2"},
+        {"accelerator": "gpu", "devices": "0,"},
+    ],
+)
+def test_trainer_gpus(monkeypatch, trainer_kwargs):
+    monkeypatch.setattr(torch.cuda, "is_available", lambda: True)
+    monkeypatch.setattr(torch.cuda, "device_count", lambda: 4)
+    trainer = Trainer(**trainer_kwargs)
+    with pytest.deprecated_call(
+        match="`Trainer.gpus` was deprecated in v1.6 and will be removed in v1.8."
+        " Please use `Trainer.num_devices` or `Trainer.device_ids` to get device information instead."
+    ):
+        assert trainer.gpus == trainer_kwargs.get("devices")