ci: add strict test evidence gates

tests/test_coverage_thresholds.py

@@ -0,0 +1,45 @@
+"""Tests for the separate line/branch coverage policy gate."""
+
+from __future__ import annotations
+
+import importlib.util
+from pathlib import Path
+
+
+SCRIPT = Path(__file__).parents[1] / "scripts" / "check_coverage_thresholds.py"
+SPEC = importlib.util.spec_from_file_location("check_coverage_thresholds", SCRIPT)
+assert SPEC is not None and SPEC.loader is not None
+MODULE = importlib.util.module_from_spec(SPEC)
+SPEC.loader.exec_module(MODULE)
+
+
+def _report(line: float = 49.0, branch: float = 36.0) -> dict[str, object]:
+    return {
+        "totals": {
+            "percent_statements_covered": line,
+            "percent_branches_covered": branch,
+        },
+    }
+
+
+def test_validate_coverage_accepts_exact_floors():
+    assert MODULE.validate_coverage(
+        _report(), min_line=49.0, min_branch=36.0,
+    ) == []
+
+
+def test_validate_coverage_reports_each_regression():
+    failures = MODULE.validate_coverage(
+        _report(line=48.9, branch=35.9), min_line=49.0, min_branch=36.0,
+    )
+
+    assert failures == [
+        "line coverage 48.90% is below the 49.00% floor",
+        "branch coverage 35.90% is below the 36.00% floor",
+    ]
+
+
+def test_validate_coverage_rejects_malformed_totals():
+    assert MODULE.validate_coverage(
+        {}, min_line=49.0, min_branch=36.0,
+    ) == ["coverage report is missing the totals object"]