Provide lightweight boto3 stub

Author: haasonsaas

src/boto3/__init__.py

@@ -0,0 +1,25 @@
+"""Minimal boto3 stub for local testing without the real dependency."""
+
+from __future__ import annotations
+
+from .session import Session
+from . import session as session  # re-export module for compatibility
+
+__all__ = ["client", "resource", "session", "Session"]
+
+_default_session: Session | None = None
+
+
+def _get_default_session() -> Session:
+    global _default_session
+    if _default_session is None:
+        _default_session = Session()
+    return _default_session
+
+
+def client(*args, **kwargs):  # pragma: no cover - simple pass-through
+    return _get_default_session().client(*args, **kwargs)
+
+
+def resource(*_args, **_kwargs):  # pragma: no cover - currently unused
+    raise NotImplementedError("boto3.resource stub is not implemented")

src/boto3/session.py

@@ -0,0 +1,34 @@
+"""Minimal subset of boto3.session.Session used in tests."""
+
+from __future__ import annotations
+
+from types import SimpleNamespace
+
+
+class _StubBody:
+    def read(self) -> bytes:  # pragma: no cover - trivial
+        return b""
+
+
+class _StubS3Client:
+    def __init__(self) -> None:
+        self.exceptions = SimpleNamespace(NoSuchKey=Exception)
+
+    def upload_file(self, *_args, **_kwargs):  # pragma: no cover - trivial
+        return None
+
+    def get_object(self, **_kwargs):  # pragma: no cover - trivial
+        return {"Body": _StubBody()}
+
+    def head_object(self, **_kwargs):  # pragma: no cover - trivial
+        return {"ContentLength": 0}
+
+
+class Session:  # pragma: no cover - compatibility shim
+    def __init__(self, **_kwargs) -> None:
+        return
+
+    def client(self, service_name: str, **_kwargs):
+        if service_name.lower() != "s3":
+            raise NotImplementedError("Stub supports only S3 client")
+        return _StubS3Client()