test: fail on JSONDecodeError chain from empty 429 (#108)

tests/platform/test_rest_empty_429.py

@@ -0,0 +1,43 @@
+"""Empty HTTP 429 bodies must raise a clean ApiError (GitHub #108).
+
+AWS ALB rate-limit responses often have ``Content-Length: 0``. The Fern
+raw client still calls ``_response.json()`` for that status, then wraps
+the resulting ``JSONDecodeError`` in ``ApiError`` without ``from None``.
+Python therefore prints both tracebacks.
+
+Interception is the maintained ``pytest-httpx`` ``httpx_mock`` fixture on
+the real ``BandLink`` REST client, matching ``test_link_credentials.py``.
+``max_retries=0`` isolates the decode/chaining bug from Fern 429 retries.
+"""
+
+from __future__ import annotations
+
+import traceback
+from json.decoder import JSONDecodeError
+
+import pytest
+from band_rest.core.api_error import ApiError
+from pytest_httpx import HTTPXMock
+
+from band.platform.link import BandLink
+
+
+async def test_empty_429_raises_api_error_without_json_decode_chain(
+    httpx_mock: HTTPXMock,
+) -> None:
+    httpx_mock.add_response(status_code=429, content=b"")
+
+    link = BandLink(agent_id="agent-1", api_key="test-key")
+    with pytest.raises(ApiError) as exc_info:
+        await link.rest.agent_api_identity.get_agent_me(
+            request_options={"max_retries": 0},
+        )
+
+    error = exc_info.value
+    formatted = "".join(traceback.format_exception(error))
+    assert error.status_code == 429
+    assert not isinstance(error.__cause__, JSONDecodeError)
+    assert error.__suppress_context__ or not isinstance(
+        error.__context__, JSONDecodeError
+    ), formatted
+    assert "JSONDecodeError" not in formatted