diff --git a/tests/test_litellm/responses/litellm_completion_transformation/test_function_call_output_adjacency.py b/tests/test_litellm/responses/litellm_completion_transformation/test_function_call_output_adjacency.py
new file mode 100644
index 00000000000..84ca0410e58
--- /dev/null
+++ b/tests/test_litellm/responses/litellm_completion_transformation/test_function_call_output_adjacency.py
@@ -0,0 +1,205 @@
+"""
+Tests for ``_reorder_function_call_outputs_adjacent``.
+
+Bedrock Converse rejects requests where a ``toolResult`` is not located in
+the ``user`` message *immediately* following the assistant message that
+emitted the matching ``toolUse``. The OpenAI Responses API itself does not
+require strict adjacency, so upstream clients can legally inject a
+``message`` between a ``function_call`` and its ``function_call_output``.
+
+The helper normalises the Responses-API input so the converted Chat
+Completions / Bedrock Converse payload always satisfies the strictest
+contract. These tests pin the helper's behaviour at the
+Responses → Chat Completions boundary.
+"""
+
+from litellm.responses.litellm_completion_transformation.transformation import (
+    LiteLLMCompletionResponsesConfig,
+)
+
+reorder = LiteLLMCompletionResponsesConfig._reorder_function_call_outputs_adjacent
+
+
+def _function_call(call_id: str, name: str = "exec_command") -> dict:
+    return {
+        "type": "function_call",
+        "call_id": call_id,
+        "name": name,
+        "arguments": "{}",
+    }
+
+
+def _function_call_output(call_id: str, output: str = "ok") -> dict:
+    return {
+        "type": "function_call_output",
+        "call_id": call_id,
+        "output": output,
+    }
+
+
+def _user_message(text: str) -> dict:
+    return {"type": "message", "role": "user", "content": text}
+
+
+def _assistant_message(text: str) -> dict:
+    return {"type": "message", "role": "assistant", "content": text}
+
+
+def test_reorder_handles_empty_input():
+    assert reorder([]) == []
+
+
+def test_reorder_passes_through_non_list_input():
+    # The helper must tolerate the non-list shapes the surrounding code
+    # may pass during validation/edge cases.
+    assert reorder(None) is None  # type: ignore[arg-type]
+
+
+def test_reorder_is_noop_when_already_adjacent():
+    items = [_function_call("c1"), _function_call_output("c1")]
+    out = reorder(items)
+    assert out == items
+
+
+def test_reorder_is_idempotent_for_already_adjacent_items():
+    items = [_function_call("c1"), _function_call_output("c1")]
+    assert reorder(reorder(items)) == items
+
+
+def test_reorder_moves_output_adjacent_to_call_when_message_is_interleaved():
+    """Reproduces the OpenAI Codex CLI ``apply_patch`` heredoc trigger.
+
+    Codex detects an ``apply_patch <<EOF`` heredoc inside an
+    ``exec_command``, short-circuits via the native ``apply_patch`` tool,
+    and inserts a user-visible warning message between the
+    ``function_call`` and the synthesised ``function_call_output``.
+
+    The helper must restore adjacency so Bedrock Converse accepts the
+    converted request.
+    """
+    apply_patch_warning = (
+        "Warning: apply_patch was requested via exec_command. Use the "
+        "apply_patch tool instead of exec_command."
+    )
+    items = [
+        _user_message("hello"),
+        _function_call("c1"),
+        _user_message(apply_patch_warning),
+        _function_call_output("c1"),
+    ]
+
+    out = reorder(items)
+
+    assert out == [
+        _user_message("hello"),
+        _function_call("c1"),
+        _function_call_output("c1"),
+        _user_message(apply_patch_warning),
+    ]
+
+
+def test_reorder_is_idempotent_after_a_real_reorder():
+    items = [
+        _function_call("c1"),
+        _user_message("interlude"),
+        _function_call_output("c1"),
+    ]
+    once = reorder(items)
+    twice = reorder(once)
+    assert twice == once
+
+
+def test_reorder_handles_multiple_interleaved_pairs():
+    items = [
+        _function_call("a"),
+        _assistant_message("thinking..."),
+        _function_call("b"),
+        _user_message("interrupt"),
+        _function_call_output("a"),
+        _function_call_output("b"),
+    ]
+
+    out = reorder(items)
+
+    def index_of(call_id: str, kind: str) -> int:
+        for i, it in enumerate(out):
+            if (
+                isinstance(it, dict)
+                and it.get("type") == kind
+                and it.get("call_id") == call_id
+            ):
+                return i
+        raise AssertionError(f"missing {kind} for {call_id}: {out!r}")
+
+    # Each function_call_output sits immediately after its matching
+    # function_call.
+    assert index_of("a", "function_call_output") == index_of("a", "function_call") + 1
+    assert index_of("b", "function_call_output") == index_of("b", "function_call") + 1
+
+
+def test_reorder_leaves_orphan_outputs_in_place():
+    """Orphan ``function_call_output`` items keep their original position.
+
+    We deliberately do *not* drop them: that's a separate concern (clients
+    sending a malformed history) and is handled in a different normalisation
+    step.
+    """
+    items = [
+        _function_call_output("orphan"),
+        _user_message("hi"),
+    ]
+    assert reorder(items) == items
+
+
+def test_reorder_tolerates_non_dict_items():
+    class Sentinel:
+        pass
+
+    items = [
+        Sentinel(),
+        _function_call("c1"),
+        _function_call_output("c1"),
+    ]
+    out = reorder(items)
+    # Sentinel is preserved at position 0; the call/output pair stays
+    # adjacent (here a no-op since they were already adjacent).
+    assert isinstance(out[0], Sentinel)
+    assert out[1] == _function_call("c1")
+    assert out[2] == _function_call_output("c1")
+
+
+def test_reorder_is_a_noop_when_no_matching_call_exists():
+    """A ``function_call_output`` whose ``call_id`` matches no preceding
+    ``function_call`` must stay where it is rather than being silently moved
+    to a wrong location.
+    """
+    items = [
+        _user_message("first"),
+        _function_call_output("ghost"),
+    ]
+    assert reorder(items) == items
+
+
+def test_reorder_keeps_relative_order_of_unrelated_items():
+    items = [
+        _user_message("u1"),
+        _function_call("c1"),
+        _assistant_message("a1"),
+        _user_message("u2"),
+        _function_call_output("c1"),
+        _assistant_message("a2"),
+    ]
+
+    out = reorder(items)
+
+    # function_call_output landed right after function_call
+    fc_idx = out.index(_function_call("c1"))
+    assert out[fc_idx + 1] == _function_call_output("c1")
+    # The other items keep their relative order
+    other = [it for it in out if it.get("type") == "message"]
+    assert other == [
+        _user_message("u1"),
+        _assistant_message("a1"),
+        _user_message("u2"),
+        _assistant_message("a2"),
+    ]