test: add Gate 3 numerical oracle contracts

tests/test_mutmut_coverage_sitecustomize.py

@@ -0,0 +1,110 @@
+"""Isolated tests for the CI-only mutmut covered-line reuse hook."""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+import subprocess
+import sys
+
+
+ROOT = Path(__file__).parents[1]
+SITECUSTOMIZE = ROOT / "scripts" / "mutmut_coverage_sitecustomize"
+
+
+def _write_fake_modules(tmp_path: Path, *, validation: str = "return None") -> None:
+    mutmut_dir = tmp_path / "mutmut"
+    scripts_dir = tmp_path / "scripts"
+    mutmut_dir.mkdir()
+    scripts_dir.mkdir()
+    (mutmut_dir / "__init__.py").write_text("", encoding="utf-8")
+    (mutmut_dir / "__main__.py").write_text(
+        "def store_lines_covered_by_tests():\n"
+        "    print('original coverage collector')\n",
+        encoding="utf-8",
+    )
+    (scripts_dir / "__init__.py").write_text("", encoding="utf-8")
+    (scripts_dir / "prepare_mutation_coverage.py").write_text(
+        "def validate_manifest():\n"
+        f"    {validation}\n"
+        "def validate_execution_manifest():\n"
+        f"    {validation}\n",
+        encoding="utf-8",
+    )
+
+
+def _run_hook_probe(tmp_path: Path, *, env_flag: bool, validation: str = "return None"):
+    _write_fake_modules(tmp_path, validation=validation)
+    env = os.environ.copy()
+    env.pop("OBLITERATUS_MUTMUT_REUSE_COVERAGE", None)
+    env["PYTHONPATH"] = f"{SITECUSTOMIZE}:{tmp_path}"
+    if env_flag:
+        env["OBLITERATUS_MUTMUT_REUSE_COVERAGE"] = "1"
+    return subprocess.run(
+        [
+            sys.executable,
+            "-c",
+            "from mutmut import __main__ as m; m.store_lines_covered_by_tests()",
+        ],
+        check=False,
+        env=env,
+        text=True,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+    )
+
+
+def test_sitecustomize_does_not_patch_without_reuse_env(tmp_path):
+    result = _run_hook_probe(tmp_path, env_flag=False)
+
+    assert result.returncode == 0
+    assert result.stdout.strip() == "original coverage collector"
+
+
+def test_sitecustomize_patches_only_with_reuse_env_and_valid_manifest(tmp_path):
+    result = _run_hook_probe(tmp_path, env_flag=True, validation="print('validated')")
+
+    assert result.returncode == 0
+    assert "validated" in result.stdout
+    assert "Reusing prepared mutmut covered-line artifacts" in result.stdout
+    assert "original coverage collector" not in result.stdout
+
+
+def test_sitecustomize_fails_closed_when_manifest_validation_fails(tmp_path):
+    result = _run_hook_probe(
+        tmp_path,
+        env_flag=True,
+        validation="raise RuntimeError('stale manifest')",
+    )
+
+    assert result.returncode != 0
+    assert "stale manifest" in result.stderr
+
+
+def test_sitecustomize_reuses_prepared_stats_when_enabled(tmp_path):
+    _write_fake_modules(tmp_path, validation="print('validated execution')")
+    env = os.environ.copy()
+    env.pop("OBLITERATUS_MUTMUT_REUSE_COVERAGE", None)
+    env["OBLITERATUS_MUTMUT_REUSE_STATS"] = "1"
+    env["PYTHONPATH"] = f"{SITECUSTOMIZE}:{tmp_path}"
+
+    result = subprocess.run(
+        [
+            sys.executable,
+            "-c",
+            (
+                "from mutmut import __main__ as m\n"
+                "m.load_stats = lambda: True\n"
+                "m.collect_or_load_stats(object())\n"
+            ),
+        ],
+        check=False,
+        env=env,
+        text=True,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+    )
+
+    assert result.returncode == 0
+    assert "validated execution" in result.stdout
+    assert "Reusing prepared mutmut test-selection stats" in result.stdout