test: clean up comments and rename file-31 test

tests/test_litellm/caching/test_partial_cache_merge.py

@@ -1,15 +1,17 @@
 """
 Regression tests for the partial-cache-hit embedding index merge bug.
 
-Exercises LLMCachingHandler._combine_cached_embedding_response_with_api_result
-directly — no provider, no Redis, no event loop needed.
+Calls _combine_cached_embedding_response_with_api_result directly with
+synthetic data without any provider, Redis, or event loop.
 """
 
 import os
 import sys
 from datetime import datetime
 
-sys.path.insert(0, os.path.abspath("../../.."))
+sys.path.insert(
+    0, os.path.abspath("../../..")
+)  # Adds the parent directory to the system path
 
 from litellm.caching.caching_handler import (
     CachingHandlerResponse,
@@ -19,29 +21,21 @@ from litellm.types.utils import Embedding, EmbeddingResponse
 
 
 def _emb(index: int, marker: int) -> Embedding:
-    """Build an Embedding with a recognisable marker so we can tell items apart."""
     return Embedding(embedding=[float(marker)], index=index, object="embedding")
 
 
 def _emb_dict(index: int, marker: int) -> dict:
-    """Dict variant — many providers (e.g. hosted_vllm) return dicts, not Embedding objects."""
+    """Dict variant; many providers (e.g. hosted_vllm) return dicts, not Embedding objects."""
     return {"embedding": [float(marker)], "index": index, "object": "embedding"}
 
 
 def _run_merge(
     batch_size: int, cache_positions: set[int], provider_as_dict: bool = False
 ) -> list[int]:
-    """
-    Simulate what the handler builds at the cache-lookup step, then call the
-    merge function with a synthetic provider response. Returns the resulting
-    indices.
-    """
     cached_data = []
     for pos in range(batch_size):
         if pos in cache_positions:
-            cached_data.append(
-                _emb(index=pos, marker=100 + pos)
-            )  # cache hits use position-based index
+            cached_data.append(_emb(index=pos, marker=100 + pos))
         else:
             cached_data.append(None)
     cached_response = EmbeddingResponse(model="x", data=cached_data, object="list")
@@ -66,19 +60,16 @@ def _run_merge(
 
 
 def test_partial_cache_hit_two_in_the_middle():
-    """File-31-style: 2 cache hits in the middle of a small batch."""
     actual = _run_merge(batch_size=8, cache_positions={1, 4})
     assert actual == [0, 1, 2, 3, 4, 5, 6, 7]
 
 
 def test_partial_cache_hit_one_at_start():
-    """One cache hit at the start shifts every following item by 1."""
     actual = _run_merge(batch_size=5, cache_positions={0})
     assert actual == [0, 1, 2, 3, 4]
 
 
 def test_partial_cache_hit_no_duplicates():
-    """All indices in the merged response must be unique."""
     for hits in ({1}, {1, 4}, {0, 2, 5}, set(range(15))):
         actual = _run_merge(batch_size=16, cache_positions=hits)
         assert len(set(actual)) == len(
@@ -87,21 +78,20 @@ def test_partial_cache_hit_no_duplicates():
 
 
 def test_all_cache_hits_no_provider_call_needed():
-    """Sanity: every position is a cache hit, indices are correct."""
     actual = _run_merge(batch_size=4, cache_positions={0, 1, 2, 3})
     assert actual == [0, 1, 2, 3]
 
 
 def test_no_cache_hits_provider_only():
-    """Sanity: nothing cached, indices are 0..N-1 from the provider directly."""
     actual = _run_merge(batch_size=4, cache_positions=set())
     assert actual == [0, 1, 2, 3]
 
 
-def test_real_world_file_31_pattern():
+def test_partial_cache_hit_large_batch():
     """
-    Exactly mirrors the observed production failure:
-    128-element batch, cache hits at positions 16 and 17 produce drift +2 from pos 18.
+    Regression test for the index drift bug: with hits at positions 16 and 17
+    in a 128-element batch, all provider items from position 18 onward received
+    an index 2 lower than their final position.
     """
     actual = _run_merge(batch_size=128, cache_positions={16, 17})
     assert actual == list(range(128))