refactor(tests): streamline transition creation in processor tests

- Replaced custom transition creation functions with a centralized `create_transition` function imported from converters across multiple test files.
- Updated test cases to utilize keyword arguments for better readability and maintainability, ensuring consistent transition creation throughout the test suite.

tests/processor/test_classifier_processor.py

@@ -31,19 +31,7 @@ from lerobot.processor import (
     NormalizerProcessorStep,
     TransitionKey,
 )
-
-
-def create_transition(observation=None, action=None, **kwargs):
-    """Helper function to create a transition dictionary."""
-    transition = {}
-    if observation is not None:
-        transition[TransitionKey.OBSERVATION] = observation
-    if action is not None:
-        transition[TransitionKey.ACTION] = action
-    for key, value in kwargs.items():
-        if hasattr(TransitionKey, key.upper()):
-            transition[getattr(TransitionKey, key.upper())] = value
-    return transition
+from lerobot.processor.converters import create_transition
 
 
 def create_default_config():
@@ -115,7 +103,8 @@ def test_classifier_processor_normalization():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(1)  # Dummy action/reward
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -146,7 +135,8 @@ def test_classifier_processor_cuda():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(1)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -157,7 +147,8 @@ def test_classifier_processor_cuda():
     assert processed[TransitionKey.ACTION].device.type == "cuda"
 
     # Process through postprocessor
-    reward_transition = create_transition(action=processed[TransitionKey.ACTION])
+    reward_transition = create_transition()
+    reward_transition[TransitionKey.ACTION] = processed[TransitionKey.ACTION]
     postprocessed = postprocessor(reward_transition)
 
     # Check that output is back on CPU
@@ -185,7 +176,8 @@ def test_classifier_processor_accelerate_scenario():
         OBS_IMAGE: torch.randn(3, 224, 224).to(device),
     }
     action = torch.randn(1).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -212,7 +204,8 @@ def test_classifier_processor_multi_gpu():
         OBS_IMAGE: torch.randn(3, 224, 224).to(device),
     }
     action = torch.randn(1).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -239,7 +232,8 @@ def test_classifier_processor_without_stats():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(1)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     processed = preprocessor(transition)
     assert processed is not None
@@ -273,7 +267,8 @@ def test_classifier_processor_save_and_load():
             OBS_IMAGE: torch.randn(3, 224, 224),
         }
         action = torch.randn(1)
-        transition = create_transition(observation, action)
+        transition = create_transition(observation=observation)
+        transition[TransitionKey.ACTION] = action
 
         processed = loaded_preprocessor(transition)
         assert processed[TransitionKey.OBSERVATION][OBS_STATE].shape == (10,)
@@ -308,7 +303,8 @@ def test_classifier_processor_mixed_precision():
         OBS_IMAGE: torch.randn(3, 224, 224, dtype=torch.float32),
     }
     action = torch.randn(1, dtype=torch.float32)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -338,7 +334,8 @@ def test_classifier_processor_batch_data():
         OBS_IMAGE: torch.randn(batch_size, 3, 224, 224),
     }
     action = torch.randn(batch_size, 1)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -363,7 +360,8 @@ def test_classifier_processor_postprocessor_identity():
 
     # Create test data for postprocessor
     reward = torch.tensor([[0.8], [0.3], [0.9]])  # Batch of rewards/predictions
-    transition = create_transition(action=reward)
+    transition = create_transition()
+    transition[TransitionKey.ACTION] = reward
 
     # Process through postprocessor
     processed = postprocessor(transition)