From 6f1e49dbc4c9be76b93f041ed9441b7a154c47f6 Mon Sep 17 00:00:00 2001
From: AdilZouitine <adilzouitinegm@gmail.com>
Date: Wed, 10 Sep 2025 13:08:44 +0200
Subject: [PATCH] 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_act_processor.py        | 53 ++++++++++----------
 tests/processor/test_batch_conversion.py     | 33 ++++++------
 tests/processor/test_batch_processor.py      | 20 ++------
 tests/processor/test_classifier_processor.py | 44 ++++++++--------
 tests/processor/test_device_processor.py     | 31 ++----------
 tests/processor/test_diffusion_processor.py  | 47 +++++++++--------
 tests/processor/test_pi0_processor.py        | 28 ++++-------
 tests/processor/test_sac_processor.py        | 52 +++++++++----------
 tests/processor/test_smolvla_processor.py    | 28 ++++-------
 tests/processor/test_vqbet_processor.py      | 47 +++++++++--------
 10 files changed, 165 insertions(+), 218 deletions(-)

diff --git a/tests/processor/test_act_processor.py b/tests/processor/test_act_processor.py
index ef3b72f54..e4c7cc734 100644
--- a/tests/processor/test_act_processor.py
+++ b/tests/processor/test_act_processor.py
@@ -33,19 +33,7 @@ from lerobot.processor import (
     TransitionKey,
     UnnormalizerProcessorStep,
 )
-
-
-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():
@@ -112,7 +100,8 @@ def test_act_processor_normalization():
     # Create test data
     observation = {OBS_STATE: torch.randn(7)}
     action = torch.randn(4)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -122,7 +111,8 @@ def test_act_processor_normalization():
     assert processed[TransitionKey.ACTION].shape == (1, 4)
 
     # Process action through postprocessor
-    action_transition = create_transition(action=processed[TransitionKey.ACTION])
+    action_transition = create_transition()
+    action_transition[TransitionKey.ACTION] = processed[TransitionKey.ACTION]
     postprocessed = postprocessor(action_transition)
 
     # Check that action is unnormalized
@@ -146,7 +136,8 @@ def test_act_processor_cuda():
     # Create CPU data
     observation = {OBS_STATE: torch.randn(7)}
     action = torch.randn(4)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -156,7 +147,8 @@ def test_act_processor_cuda():
     assert processed[TransitionKey.ACTION].device.type == "cuda"
 
     # Process through postprocessor
-    action_transition = create_transition(action=processed[TransitionKey.ACTION])
+    action_transition = create_transition()
+    action_transition[TransitionKey.ACTION] = processed[TransitionKey.ACTION]
     postprocessed = postprocessor(action_transition)
 
     # Check that action is back on CPU
@@ -181,7 +173,8 @@ def test_act_processor_accelerate_scenario():
     device = torch.device("cuda:0")
     observation = {OBS_STATE: torch.randn(1, 7).to(device)}  # Already batched and on GPU
     action = torch.randn(1, 4).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -204,7 +197,8 @@ def test_act_processor_multi_gpu():
     device = torch.device("cuda:1")
     observation = {OBS_STATE: torch.randn(1, 7).to(device)}
     action = torch.randn(1, 4).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -227,7 +221,8 @@ def test_act_processor_without_stats():
     # Process should still work (but won't normalize without stats)
     observation = {OBS_STATE: torch.randn(7)}
     action = torch.randn(4)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     processed = preprocessor(transition)
     assert processed is not None
@@ -257,7 +252,8 @@ def test_act_processor_save_and_load():
         # Test that loaded processor works
         observation = {OBS_STATE: torch.randn(7)}
         action = torch.randn(4)
-        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 == (1, 7)
@@ -281,7 +277,8 @@ def test_act_processor_device_placement_preservation():
     # Process CPU data
     observation = {OBS_STATE: torch.randn(7)}
     action = torch.randn(4)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     processed = preprocessor(transition)
     assert processed[TransitionKey.OBSERVATION][OBS_STATE].device.type == "cpu"
@@ -326,7 +323,8 @@ def test_act_processor_mixed_precision():
     # Create test data
     observation = {OBS_STATE: torch.randn(7, dtype=torch.float32)}
     action = torch.randn(4, dtype=torch.float32)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -351,7 +349,8 @@ def test_act_processor_batch_consistency():
     # Test single sample (unbatched)
     observation = {OBS_STATE: torch.randn(7)}
     action = torch.randn(4)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     processed = preprocessor(transition)
     assert processed[TransitionKey.OBSERVATION][OBS_STATE].shape[0] == 1  # Batched
@@ -359,7 +358,8 @@ def test_act_processor_batch_consistency():
     # Test already batched data
     observation_batched = {OBS_STATE: torch.randn(8, 7)}  # Batch of 8
     action_batched = torch.randn(8, 4)
-    transition_batched = create_transition(observation_batched, action_batched)
+    transition_batched = create_transition(observation=observation_batched)
+    transition_batched[TransitionKey.ACTION] = action_batched
 
     processed_batched = preprocessor(transition_batched)
     assert processed_batched[TransitionKey.OBSERVATION][OBS_STATE].shape[0] == 8
@@ -407,7 +407,8 @@ def test_act_processor_bfloat16_device_float32_normalizer():
     # Create test data
     observation = {OBS_STATE: torch.randn(7, dtype=torch.float32)}  # Start with float32
     action = torch.randn(4, dtype=torch.float32)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through full pipeline
     processed = preprocessor(transition)
diff --git a/tests/processor/test_batch_conversion.py b/tests/processor/test_batch_conversion.py
index 8d1f5e20e..8635c39e9 100644
--- a/tests/processor/test_batch_conversion.py
+++ b/tests/processor/test_batch_conversion.py
@@ -1,3 +1,5 @@
+from typing import Any
+
 import torch
 
 from lerobot.processor import DataProcessorPipeline, TransitionKey
@@ -20,7 +22,7 @@ def _dummy_batch():
 
 def test_observation_grouping_roundtrip():
     """Test that observation.* keys are properly grouped and ungrouped."""
-    proc = DataProcessorPipeline([])
+    proc = DataProcessorPipeline[dict[str, Any]]([])
     batch_in = _dummy_batch()
     batch_out = proc(batch_in)
 
@@ -45,11 +47,12 @@ def test_observation_grouping_roundtrip():
 
 def test_batch_to_transition_observation_grouping():
     """Test that batch_to_transition correctly groups observation.* keys."""
+    base_batch = _dummy_batch()
     batch = {
         "observation.image.top": torch.randn(1, 3, 128, 128),
-        "observation.image.left": torch.randn(1, 3, 128, 128),
+        "observation.image.left": base_batch["observation.image.left"],
         "observation.state": [1, 2, 3, 4],
-        "action": "action_data",
+        "action": torch.tensor([[0.1, 0.2]]),
         "next.reward": 1.5,
         "next.done": True,
         "next.truncated": False,
@@ -74,7 +77,7 @@ def test_batch_to_transition_observation_grouping():
     assert transition[TransitionKey.OBSERVATION]["observation.state"] == [1, 2, 3, 4]
 
     # Check other fields
-    assert transition[TransitionKey.ACTION] == "action_data"
+    assert torch.allclose(transition[TransitionKey.ACTION], torch.tensor([[0.1, 0.2]]))
     assert transition[TransitionKey.REWARD] == 1.5
     assert transition[TransitionKey.DONE]
     assert not transition[TransitionKey.TRUNCATED]
@@ -84,15 +87,16 @@ def test_batch_to_transition_observation_grouping():
 
 def test_transition_to_batch_observation_flattening():
     """Test that transition_to_batch correctly flattens observation dict."""
+    base_batch = _dummy_batch()
     observation_dict = {
         "observation.image.top": torch.randn(1, 3, 128, 128),
-        "observation.image.left": torch.randn(1, 3, 128, 128),
+        "observation.image.left": base_batch["observation.image.left"],
         "observation.state": [1, 2, 3, 4],
     }
 
     transition = {
         TransitionKey.OBSERVATION: observation_dict,
-        TransitionKey.ACTION: "action_data",
+        TransitionKey.ACTION: torch.tensor([[0.3, 0.4]]),
         TransitionKey.REWARD: 1.5,
         TransitionKey.DONE: True,
         TransitionKey.TRUNCATED: False,
@@ -113,7 +117,7 @@ def test_transition_to_batch_observation_flattening():
     assert batch["observation.state"] == [1, 2, 3, 4]
 
     # Check other fields are mapped to next.* format
-    assert batch["action"] == "action_data"
+    assert torch.allclose(batch["action"], torch.tensor([[0.3, 0.4]]))
     assert batch["next.reward"] == 1.5
     assert batch["next.done"]
     assert not batch["next.truncated"]
@@ -123,7 +127,7 @@ def test_transition_to_batch_observation_flattening():
 def test_no_observation_keys():
     """Test behavior when there are no observation.* keys."""
     batch = {
-        "action": "action_data",
+        "action": torch.tensor([[0.7, 0.8]]),
         "next.reward": 2.0,
         "next.done": False,
         "next.truncated": True,
@@ -136,7 +140,7 @@ def test_no_observation_keys():
     assert transition[TransitionKey.OBSERVATION] is None
 
     # Check other fields
-    assert transition[TransitionKey.ACTION] == "action_data"
+    assert torch.allclose(transition[TransitionKey.ACTION], torch.tensor([[0.7, 0.8]]))
     assert transition[TransitionKey.REWARD] == 2.0
     assert not transition[TransitionKey.DONE]
     assert transition[TransitionKey.TRUNCATED]
@@ -144,7 +148,7 @@ def test_no_observation_keys():
 
     # Round trip should work
     reconstructed_batch = transition_to_batch(transition)
-    assert reconstructed_batch["action"] == "action_data"
+    assert torch.allclose(reconstructed_batch["action"], torch.tensor([[0.7, 0.8]]))
     assert reconstructed_batch["next.reward"] == 2.0
     assert not reconstructed_batch["next.done"]
     assert reconstructed_batch["next.truncated"]
@@ -153,13 +157,13 @@ def test_no_observation_keys():
 
 def test_minimal_batch():
     """Test with minimal batch containing only observation.* and action."""
-    batch = {"observation.state": "minimal_state", "action": "minimal_action"}
+    batch = {"observation.state": "minimal_state", "action": torch.tensor([[0.9]])}
 
     transition = batch_to_transition(batch)
 
     # Check observation
     assert transition[TransitionKey.OBSERVATION] == {"observation.state": "minimal_state"}
-    assert transition[TransitionKey.ACTION] == "minimal_action"
+    assert torch.allclose(transition[TransitionKey.ACTION], torch.tensor([[0.9]]))
 
     # Check defaults
     assert transition[TransitionKey.REWARD] == 0.0
@@ -171,7 +175,7 @@ def test_minimal_batch():
     # Round trip
     reconstructed_batch = transition_to_batch(transition)
     assert reconstructed_batch["observation.state"] == "minimal_state"
-    assert reconstructed_batch["action"] == "minimal_action"
+    assert torch.allclose(reconstructed_batch["action"], torch.tensor([[0.9]]))
     assert reconstructed_batch["next.reward"] == 0.0
     assert not reconstructed_batch["next.done"]
     assert not reconstructed_batch["next.truncated"]
@@ -204,9 +208,10 @@ def test_empty_batch():
 
 def test_complex_nested_observation():
     """Test with complex nested observation data."""
+    base_batch = _dummy_batch()
     batch = {
         "observation.image.top": {"image": torch.randn(1, 3, 128, 128), "timestamp": 1234567890},
-        "observation.image.left": {"image": torch.randn(1, 3, 128, 128), "timestamp": 1234567891},
+        "observation.image.left": {"image": base_batch["observation.image.left"], "timestamp": 1234567891},
         "observation.state": torch.randn(7),
         "action": torch.randn(8),
         "next.reward": 3.14,
diff --git a/tests/processor/test_batch_processor.py b/tests/processor/test_batch_processor.py
index 568bfa5c4..371ef4ae7 100644
--- a/tests/processor/test_batch_processor.py
+++ b/tests/processor/test_batch_processor.py
@@ -28,21 +28,7 @@ from lerobot.processor import (
     ProcessorStepRegistry,
     TransitionKey,
 )
-
-
-def create_transition(
-    observation=None, action=None, reward=None, done=None, truncated=None, info=None, complementary_data=None
-):
-    """Helper to create an EnvTransition dictionary."""
-    return {
-        TransitionKey.OBSERVATION: observation,
-        TransitionKey.ACTION: action,
-        TransitionKey.REWARD: reward,
-        TransitionKey.DONE: done,
-        TransitionKey.TRUNCATED: truncated,
-        TransitionKey.INFO: info,
-        TransitionKey.COMPLEMENTARY_DATA: complementary_data,
-    }
+from lerobot.processor.converters import create_transition
 
 
 def test_state_1d_to_2d():
@@ -517,7 +503,7 @@ def test_action_non_tensor():
     assert np.array_equal(result[TransitionKey.ACTION], action_numpy)
 
     # String action (edge case)
-    action_string = "forward"
+    action_string = "eef.pos.x"
     transition = create_transition(action=action_string)
     result = processor(transition)
     assert result[TransitionKey.ACTION] == action_string
@@ -703,7 +689,7 @@ def test_complementary_data_none():
     transition = create_transition(complementary_data=None)
     result = processor(transition)
 
-    assert result[TransitionKey.COMPLEMENTARY_DATA] is None
+    assert result[TransitionKey.COMPLEMENTARY_DATA] == {}
 
 
 def test_complementary_data_empty():
diff --git a/tests/processor/test_classifier_processor.py b/tests/processor/test_classifier_processor.py
index 1c9118bd1..11540b8d5 100644
--- a/tests/processor/test_classifier_processor.py
+++ b/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)
diff --git a/tests/processor/test_device_processor.py b/tests/processor/test_device_processor.py
index 113b1adf2..56de52774 100644
--- a/tests/processor/test_device_processor.py
+++ b/tests/processor/test_device_processor.py
@@ -20,28 +20,7 @@ import torch
 
 from lerobot.configs.types import FeatureType, PipelineFeatureType, PolicyFeature
 from lerobot.processor import DataProcessorPipeline, DeviceProcessorStep, TransitionKey
-
-
-def create_transition(
-    observation=None, action=None, reward=None, done=None, truncated=None, info=None, complementary_data=None
-):
-    """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
-    if reward is not None:
-        transition[TransitionKey.REWARD] = reward
-    if done is not None:
-        transition[TransitionKey.DONE] = done
-    if truncated is not None:
-        transition[TransitionKey.TRUNCATED] = truncated
-    if info is not None:
-        transition[TransitionKey.INFO] = info
-    if complementary_data is not None:
-        transition[TransitionKey.COMPLEMENTARY_DATA] = complementary_data
-    return transition
+from lerobot.processor.converters import create_transition
 
 
 def test_basic_functionality():
@@ -147,14 +126,14 @@ def test_none_values():
     # Test with None observation
     transition = create_transition(observation=None, action=torch.randn(5))
     result = processor(transition)
-    assert TransitionKey.OBSERVATION not in result
+    assert result[TransitionKey.OBSERVATION] is None
     assert result[TransitionKey.ACTION].device.type == "cpu"
 
     # Test with None action
     transition = create_transition(observation={"observation.state": torch.randn(10)}, action=None)
     result = processor(transition)
     assert result[TransitionKey.OBSERVATION]["observation.state"].device.type == "cpu"
-    assert TransitionKey.ACTION not in result
+    assert result[TransitionKey.ACTION] is None
 
 
 def test_empty_observation():
@@ -822,8 +801,8 @@ def test_complementary_data_none():
 
     result = processor(transition)
 
-    # Complementary data should not be in the result (same as input)
-    assert TransitionKey.COMPLEMENTARY_DATA not in result
+    # Complementary data should be an empty dict (standardized behavior)
+    assert result[TransitionKey.COMPLEMENTARY_DATA] == {}
 
 
 @pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA not available")
diff --git a/tests/processor/test_diffusion_processor.py b/tests/processor/test_diffusion_processor.py
index 1e5e93b4d..e032f3e3d 100644
--- a/tests/processor/test_diffusion_processor.py
+++ b/tests/processor/test_diffusion_processor.py
@@ -33,19 +33,7 @@ from lerobot.processor import (
     TransitionKey,
     UnnormalizerProcessorStep,
 )
-
-
-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():
@@ -118,7 +106,8 @@ def test_diffusion_processor_with_images():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(6)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -149,7 +138,8 @@ def test_diffusion_processor_cuda():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(6)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -160,7 +150,8 @@ def test_diffusion_processor_cuda():
     assert processed[TransitionKey.ACTION].device.type == "cuda"
 
     # Process through postprocessor
-    action_transition = create_transition(action=processed[TransitionKey.ACTION])
+    action_transition = create_transition()
+    action_transition[TransitionKey.ACTION] = processed[TransitionKey.ACTION]
     postprocessed = postprocessor(action_transition)
 
     # Check that action is back on CPU
@@ -188,7 +179,8 @@ def test_diffusion_processor_accelerate_scenario():
         OBS_IMAGE: torch.randn(1, 3, 224, 224).to(device),
     }
     action = torch.randn(1, 6).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -215,7 +207,8 @@ def test_diffusion_processor_multi_gpu():
         OBS_IMAGE: torch.randn(1, 3, 224, 224).to(device),
     }
     action = torch.randn(1, 6).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -242,7 +235,8 @@ def test_diffusion_processor_without_stats():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(6)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     processed = preprocessor(transition)
     assert processed is not None
@@ -276,7 +270,8 @@ def test_diffusion_processor_save_and_load():
             OBS_IMAGE: torch.randn(3, 224, 224),
         }
         action = torch.randn(6)
-        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 == (1, 7)
@@ -322,7 +317,8 @@ def test_diffusion_processor_mixed_precision():
         OBS_IMAGE: torch.randn(3, 224, 224, dtype=torch.float32),
     }
     action = torch.randn(6, dtype=torch.float32)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -352,7 +348,8 @@ def test_diffusion_processor_identity_normalization():
         OBS_IMAGE: image_value.clone(),
     }
     action = torch.randn(6)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -381,7 +378,8 @@ def test_diffusion_processor_batch_consistency():
             OBS_IMAGE: torch.randn(batch_size, 3, 224, 224) if batch_size > 1 else torch.randn(3, 224, 224),
         }
         action = torch.randn(batch_size, 6) if batch_size > 1 else torch.randn(6)
-        transition = create_transition(observation, action)
+        transition = create_transition(observation=observation)
+        transition[TransitionKey.ACTION] = action
 
         processed = preprocessor(transition)
 
@@ -435,7 +433,8 @@ def test_diffusion_processor_bfloat16_device_float32_normalizer():
         OBS_IMAGE: torch.randn(3, 224, 224, dtype=torch.float32),
     }
     action = torch.randn(6, dtype=torch.float32)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through full pipeline
     processed = preprocessor(transition)
diff --git a/tests/processor/test_pi0_processor.py b/tests/processor/test_pi0_processor.py
index e83635a48..6c87f826b 100644
--- a/tests/processor/test_pi0_processor.py
+++ b/tests/processor/test_pi0_processor.py
@@ -34,6 +34,7 @@ from lerobot.processor import (
     TransitionKey,
     UnnormalizerProcessorStep,
 )
+from lerobot.processor.converters import create_transition
 
 
 class MockTokenizerProcessorStep(ProcessorStep):
@@ -52,21 +53,6 @@ class MockTokenizerProcessorStep(ProcessorStep):
         return features
 
 
-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
-        elif key == "complementary_data":
-            transition[TransitionKey.COMPLEMENTARY_DATA] = value
-    return transition
-
-
 def create_default_config():
     """Create a default PI0 configuration for testing."""
     config = PI0Config()
@@ -219,7 +205,8 @@ def test_pi0_processor_cuda():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(6)
-    transition = create_transition(observation, action, complementary_data={"task": "test task"})
+    transition = create_transition(observation=observation, complementary_data={"task": "test task"})
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -275,7 +262,8 @@ def test_pi0_processor_accelerate_scenario():
         OBS_IMAGE: torch.randn(1, 3, 224, 224).to(device),
     }
     action = torch.randn(1, 6).to(device)
-    transition = create_transition(observation, action, complementary_data={"task": ["test task"]})
+    transition = create_transition(observation=observation, complementary_data={"task": ["test task"]})
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -331,7 +319,8 @@ def test_pi0_processor_multi_gpu():
         OBS_IMAGE: torch.randn(1, 3, 224, 224).to(device),
     }
     action = torch.randn(1, 6).to(device)
-    transition = create_transition(observation, action, complementary_data={"task": ["test task"]})
+    transition = create_transition(observation=observation, complementary_data={"task": ["test task"]})
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -426,8 +415,9 @@ def test_pi0_processor_bfloat16_device_float32_normalizer():
     }
     action = torch.randn(6, dtype=torch.float32)  # PI0 expects size 6
     transition = create_transition(
-        observation, action, complementary_data={"task": "test bfloat16 adaptation"}
+        observation=observation, complementary_data={"task": "test bfloat16 adaptation"}
     )
+    transition[TransitionKey.ACTION] = action
 
     # Process through full pipeline
     processed = preprocessor(transition)
diff --git a/tests/processor/test_sac_processor.py b/tests/processor/test_sac_processor.py
index 3e26172c3..9fbe7979b 100644
--- a/tests/processor/test_sac_processor.py
+++ b/tests/processor/test_sac_processor.py
@@ -33,19 +33,7 @@ from lerobot.processor import (
     TransitionKey,
     UnnormalizerProcessorStep,
 )
-
-
-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():
@@ -117,7 +105,8 @@ def test_sac_processor_normalization_modes():
     # Create test data
     observation = {OBS_STATE: torch.randn(10) * 2}  # Larger values to test normalization
     action = torch.rand(5) * 2 - 1  # Range [-1, 1]
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -129,7 +118,8 @@ def test_sac_processor_normalization_modes():
     assert processed[TransitionKey.ACTION].shape == (1, 5)
 
     # Process action through postprocessor
-    action_transition = create_transition(action=processed[TransitionKey.ACTION])
+    action_transition = create_transition()
+    action_transition[TransitionKey.ACTION] = processed[TransitionKey.ACTION]
     postprocessed = postprocessor(action_transition)
 
     # Check that action is unnormalized (but still batched)
@@ -153,7 +143,8 @@ def test_sac_processor_cuda():
     # Create CPU data
     observation = {OBS_STATE: torch.randn(10)}
     action = torch.randn(5)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -163,7 +154,8 @@ def test_sac_processor_cuda():
     assert processed[TransitionKey.ACTION].device.type == "cuda"
 
     # Process through postprocessor
-    action_transition = create_transition(action=processed[TransitionKey.ACTION])
+    action_transition = create_transition()
+    action_transition[TransitionKey.ACTION] = processed[TransitionKey.ACTION]
     postprocessed = postprocessor(action_transition)
 
     # Check that action is back on CPU
@@ -188,7 +180,8 @@ def test_sac_processor_accelerate_scenario():
     device = torch.device("cuda:0")
     observation = {OBS_STATE: torch.randn(10).to(device)}
     action = torch.randn(5).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -216,7 +209,8 @@ def test_sac_processor_multi_gpu():
     device = torch.device("cuda:1")
     observation = {OBS_STATE: torch.randn(10).to(device)}
     action = torch.randn(5).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -254,7 +248,8 @@ def test_sac_processor_without_stats():
     # Process should still work
     observation = {OBS_STATE: torch.randn(10)}
     action = torch.randn(5)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     processed = preprocessor(transition)
     assert processed is not None
@@ -284,7 +279,8 @@ def test_sac_processor_save_and_load():
         # Test that loaded processor works
         observation = {OBS_STATE: torch.randn(10)}
         action = torch.randn(5)
-        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 == (1, 10)
@@ -329,7 +325,8 @@ def test_sac_processor_mixed_precision():
     # Create test data
     observation = {OBS_STATE: torch.randn(10, dtype=torch.float32)}
     action = torch.randn(5, dtype=torch.float32)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -355,7 +352,8 @@ def test_sac_processor_batch_data():
     batch_size = 32
     observation = {OBS_STATE: torch.randn(batch_size, 10)}
     action = torch.randn(batch_size, 5)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -378,13 +376,14 @@ def test_sac_processor_edge_cases():
     )
 
     # Test with empty observation
-    transition = create_transition(observation={}, action=torch.randn(5))
+    transition = create_transition(observation={})
+    transition[TransitionKey.ACTION] = torch.randn(5)
     processed = preprocessor(transition)
     assert processed[TransitionKey.OBSERVATION] == {}
     assert processed[TransitionKey.ACTION].shape == (1, 5)
 
     # Test with None action
-    transition = create_transition(observation={OBS_STATE: torch.randn(10)}, action=None)
+    transition = create_transition(observation={OBS_STATE: torch.randn(10)})
     processed = preprocessor(transition)
     assert processed[TransitionKey.OBSERVATION][OBS_STATE].shape == (1, 10)
     # When action is None, it may still be present with None value
@@ -433,7 +432,8 @@ def test_sac_processor_bfloat16_device_float32_normalizer():
     # Create test data
     observation = {OBS_STATE: torch.randn(10, dtype=torch.float32)}  # Start with float32
     action = torch.randn(5, dtype=torch.float32)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through full pipeline
     processed = preprocessor(transition)
diff --git a/tests/processor/test_smolvla_processor.py b/tests/processor/test_smolvla_processor.py
index 317b0feec..944901977 100644
--- a/tests/processor/test_smolvla_processor.py
+++ b/tests/processor/test_smolvla_processor.py
@@ -37,6 +37,7 @@ from lerobot.processor import (
     TransitionKey,
     UnnormalizerProcessorStep,
 )
+from lerobot.processor.converters import create_transition
 
 
 class MockTokenizerProcessorStep(ProcessorStep):
@@ -55,21 +56,6 @@ class MockTokenizerProcessorStep(ProcessorStep):
         return features
 
 
-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
-        elif key == "complementary_data":
-            transition[TransitionKey.COMPLEMENTARY_DATA] = value
-    return transition
-
-
 def create_default_config():
     """Create a default SmolVLA configuration for testing."""
     config = SmolVLAConfig()
@@ -228,7 +214,8 @@ def test_smolvla_processor_cuda():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(7)
-    transition = create_transition(observation, action, complementary_data={"task": "test task"})
+    transition = create_transition(observation=observation, complementary_data={"task": "test task"})
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -286,7 +273,8 @@ def test_smolvla_processor_accelerate_scenario():
         OBS_IMAGE: torch.randn(1, 3, 224, 224).to(device),
     }
     action = torch.randn(1, 7).to(device)
-    transition = create_transition(observation, action, complementary_data={"task": ["test task"]})
+    transition = create_transition(observation=observation, complementary_data={"task": ["test task"]})
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -344,7 +332,8 @@ def test_smolvla_processor_multi_gpu():
         OBS_IMAGE: torch.randn(1, 3, 224, 224).to(device),
     }
     action = torch.randn(1, 7).to(device)
-    transition = create_transition(observation, action, complementary_data={"task": ["test task"]})
+    transition = create_transition(observation=observation, complementary_data={"task": ["test task"]})
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -455,8 +444,9 @@ def test_smolvla_processor_bfloat16_device_float32_normalizer():
     }
     action = torch.randn(7, dtype=torch.float32)
     transition = create_transition(
-        observation, action, complementary_data={"task": "test bfloat16 adaptation"}
+        observation=observation, complementary_data={"task": "test bfloat16 adaptation"}
     )
+    transition[TransitionKey.ACTION] = action
 
     # Process through full pipeline
     processed = preprocessor(transition)
diff --git a/tests/processor/test_vqbet_processor.py b/tests/processor/test_vqbet_processor.py
index c05fb15fe..fdfc62a76 100644
--- a/tests/processor/test_vqbet_processor.py
+++ b/tests/processor/test_vqbet_processor.py
@@ -33,19 +33,7 @@ from lerobot.processor import (
     TransitionKey,
     UnnormalizerProcessorStep,
 )
-
-
-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():
@@ -123,7 +111,8 @@ def test_vqbet_processor_with_images():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(7)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -154,7 +143,8 @@ def test_vqbet_processor_cuda():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(7)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -165,7 +155,8 @@ def test_vqbet_processor_cuda():
     assert processed[TransitionKey.ACTION].device.type == "cuda"
 
     # Process through postprocessor
-    action_transition = create_transition(action=processed[TransitionKey.ACTION])
+    action_transition = create_transition()
+    action_transition[TransitionKey.ACTION] = processed[TransitionKey.ACTION]
     postprocessed = postprocessor(action_transition)
 
     # Check that action is back on CPU
@@ -193,7 +184,8 @@ def test_vqbet_processor_accelerate_scenario():
         OBS_IMAGE: torch.randn(1, 3, 224, 224).to(device),
     }
     action = torch.randn(1, 7).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -225,7 +217,8 @@ def test_vqbet_processor_multi_gpu():
         OBS_IMAGE: torch.randn(1, 3, 224, 224).to(device),
     }
     action = torch.randn(1, 7).to(device)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -267,7 +260,8 @@ def test_vqbet_processor_without_stats():
         OBS_IMAGE: torch.randn(3, 224, 224),
     }
     action = torch.randn(7)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     processed = preprocessor(transition)
     assert processed is not None
@@ -300,7 +294,8 @@ def test_vqbet_processor_save_and_load():
             OBS_IMAGE: torch.randn(3, 224, 224),
         }
         action = torch.randn(7)
-        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 == (1, 8)
@@ -349,7 +344,8 @@ def test_vqbet_processor_mixed_precision():
         OBS_IMAGE: torch.randn(3, 224, 224, dtype=torch.float32),
     }
     action = torch.randn(7, dtype=torch.float32)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -379,7 +375,8 @@ def test_vqbet_processor_large_batch():
         OBS_IMAGE: torch.randn(batch_size, 3, 224, 224),
     }
     action = torch.randn(batch_size, 7)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through preprocessor
     processed = preprocessor(transition)
@@ -410,7 +407,8 @@ def test_vqbet_processor_sequential_processing():
             OBS_IMAGE: torch.randn(3, 224, 224),
         }
         action = torch.randn(7)
-        transition = create_transition(observation, action)
+        transition = create_transition(observation=observation)
+        transition[TransitionKey.ACTION] = action
 
         processed = preprocessor(transition)
         results.append(processed)
@@ -467,7 +465,8 @@ def test_vqbet_processor_bfloat16_device_float32_normalizer():
         OBS_IMAGE: torch.randn(3, 224, 224, dtype=torch.float32),
     }
     action = torch.randn(7, dtype=torch.float32)
-    transition = create_transition(observation, action)
+    transition = create_transition(observation=observation)
+    transition[TransitionKey.ACTION] = action
 
     # Process through full pipeline
     processed = preprocessor(transition)