test: add pytest scaffolding

tests/conftest.py

@@ -0,0 +1,22 @@
+"""Shared pytest fixtures.
+
+The default pytest config (pyproject.toml) skips tests marked `gpu`. Opt in
+to GPU smoke tests with `pytest -m gpu`.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+from pathlib import Path
+
+import pytest
+
+# Ensure repo root is importable as flat modules (matches z-image-studio convention).
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+
+
+@pytest.fixture(autouse=True)
+def _silence_mps_fallback_env(monkeypatch):
+    """L1+L2 tests don't touch torch/mps; clear the env so test logs are clean."""
+    monkeypatch.delenv("PYTORCH_ENABLE_MPS_FALLBACK", raising=False)