test(processor): all processors use now the same create_transition (#1906)

* test(processor): all processors use now the same create_transition

* test(processor): use identity instead of lambda for transition in pipelines

tests/processor/test_rename_processor.py

@@ -26,25 +26,11 @@ from lerobot.processor import (
     RenameObservationsProcessorStep,
     TransitionKey,
 )
+from lerobot.processor.converters import create_transition, identity_transition
 from lerobot.processor.rename_processor import rename_stats
 from tests.conftest import assert_contract_is_typed
 
 
-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,
-    }
-
-
 def test_basic_renaming():
     """Test basic key renaming functionality."""
     rename_map = {
@@ -193,7 +179,9 @@ def test_integration_with_robot_processor():
     }
     rename_processor = RenameObservationsProcessorStep(rename_map=rename_map)
 
-    pipeline = DataProcessorPipeline([rename_processor], to_transition=lambda x: x, to_output=lambda x: x)
+    pipeline = DataProcessorPipeline(
+        [rename_processor], to_transition=identity_transition, to_output=identity_transition
+    )
 
     observation = {
         "agent_pos": np.array([1.0, 2.0, 3.0]),
@@ -244,7 +232,7 @@ def test_save_and_load_pretrained():
 
         # Load pipeline
         loaded_pipeline = DataProcessorPipeline.from_pretrained(
-            tmp_dir, to_transition=lambda x: x, to_output=lambda x: x
+            tmp_dir, to_transition=identity_transition, to_output=identity_transition
         )
 
         assert loaded_pipeline.name == "TestRenameProcessorStep"
@@ -286,7 +274,9 @@ def test_registry_functionality():
 def test_registry_based_save_load():
     """Test save/load using registry name instead of module path."""
     processor = RenameObservationsProcessorStep(rename_map={"key1": "renamed_key1"})
-    pipeline = DataProcessorPipeline([processor], to_transition=lambda x: x, to_output=lambda x: x)
+    pipeline = DataProcessorPipeline(
+        [processor], to_transition=identity_transition, to_output=identity_transition
+    )
 
     with tempfile.TemporaryDirectory() as tmp_dir:
         # Save and load
@@ -328,7 +318,7 @@ def test_chained_rename_processors():
     )
 
     pipeline = DataProcessorPipeline(
-        [processor1, processor2], to_transition=lambda x: x, to_output=lambda x: x
+        [processor1, processor2], to_transition=identity_transition, to_output=identity_transition
     )
 
     observation = {