Fix test device for buffers (#1993)

* Prevent test_device from being a noop

* Update changelog

---------

Co-authored-by: Adrià Garriga-Alonso <adria@far.ai>

docs/misc/changelog.rst

@@ -30,6 +30,8 @@ Bug Fixes:
 - Fixed error when loading a model that has ``net_arch`` manually set to ``None``   (@jak3122)
 - Set requirement numpy<2.0 until PyTorch is compatible (https://github.com/pytorch/pytorch/issues/107302)
 - Updated DQN optimizer input to only include q_network parameters, removing the target_q_network ones (@corentinlger)
+- Fixed ``test_buffers.py::test_device`` which was not actually checking the device of tensors (@rhaps0dy)
+
 
 `SB3-Contrib`_
 ^^^^^^^^^^^^^^

tests/test_buffers.py

@@ -139,18 +139,25 @@ def test_device_buffer(replay_buffer_cls, device):
 
     # Get data from the buffer
     if replay_buffer_cls in [RolloutBuffer, DictRolloutBuffer]:
+        # get returns an iterator over minibatches
         data = buffer.get(50)
     elif replay_buffer_cls in [ReplayBuffer, DictReplayBuffer]:
-        data = buffer.sample(50)
+        data = [buffer.sample(50)]
 
     # Check that all data are on the desired device
     desired_device = get_device(device).type
-    for value in list(data):
-        if isinstance(value, dict):
-            for key in value.keys():
-                assert value[key].device.type == desired_device
-        elif isinstance(value, th.Tensor):
-            assert value.device.type == desired_device
+    for minibatch in list(data):
+        for value in minibatch:
+            if isinstance(value, dict):
+                for key in value.keys():
+                    assert value[key].device.type == desired_device
+            elif isinstance(value, th.Tensor):
+                assert value.device.type == desired_device
+            elif isinstance(value, np.ndarray):
+                # For prioritized replay weights/indices
+                pass
+            else:
+                raise TypeError(f"Unknown value type: {type(value)}")
 
 
 def test_custom_rollout_buffer():