Add a test to validate that cfgv.WarnAdditionalKeys working as expected in the relevant config schemas

pre_commit/clientlib.py

@@ -109,6 +109,8 @@ META = 'meta'
 
 
 class MigrateShaToRev(object):
+    key = 'rev'
+
     @staticmethod
     def _cond(key):
         return cfgv.Conditional(
@@ -263,7 +265,14 @@ CONFIG_SCHEMA = cfgv.Map(
         '0',
     ),
     cfgv.WarnAdditionalKeys(
-        ('repos',),
+        (
+            'repos',
+            'default_language_version',
+            'default_stages',
+            'exclude',
+            'fail_fast',
+            'minimum_pre_commit_version',
+        ),
         warn_on_unknown_keys_at_top_level,
     ),
 )

tests/clientlib_test.py

@@ -305,3 +305,12 @@ def test_minimum_pre_commit_version_failing():
 def test_minimum_pre_commit_version_passing():
     cfg = {'repos': [], 'minimum_pre_commit_version': '0'}
     cfgv.validate(cfg, CONFIG_SCHEMA)
+
+
+@pytest.mark.parametrize('schema', (CONFIG_SCHEMA, CONFIG_REPO_DICT))
+def test_warn_additional(schema):
+    allowed_keys = {item.key for item in schema.items if hasattr(item, 'key')}
+    warn_additional, = [
+        x for x in schema.items if isinstance(x, cfgv.WarnAdditionalKeys)
+    ]
+    assert allowed_keys == set(warn_additional.keys)