Gate on full config_db table coverage

tests/unit/e2e/test_coverage.py

@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: Apache-2.0
+
+"""Gate on the golden set covering every config_db table the generator emits.
+
+tests/e2e/coverage.py is the human-facing report; this is the check that
+actually fails. It lives in the unit suite rather than in the E2E job because
+it needs neither NetBox nor a generated config -- only the generator source
+and the committed goldens -- so it costs milliseconds and runs on every
+change, instead of only when the E2E job's file matcher fires.
+
+What it catches is the one coverage failure nothing else does: a newly
+emitted table that arrives with no golden. Coverage going the other way (a
+table that had a golden becoming empty) already fails the golden comparison,
+because the golden file itself changes.
+"""
+
+from tests.e2e.coverage import covered_tables, emitted_tables
+
+
+def test_every_emitted_table_has_golden_coverage():
+    missing = sorted(emitted_tables() - covered_tables())
+
+    assert not missing, (
+        "the generator can emit these config_db tables, but they are empty in "
+        "every file under tests/e2e/golden/: " + ", ".join(missing) + ". Seed a "
+        "device that populates them under tests/e2e/scenario/resources/ and "
+        "rewrite the goldens with `make sonic-e2e-regen`, or -- if the table "
+        "cannot be reached by any fixture -- exclude it here with a comment "
+        "saying why."
+    )