Write test for auto-validating manifest at root of repo

tests/clientlib/validate_manifest_test.py

@@ -3,7 +3,9 @@ import __builtin__
 import jsonschema
 import pytest
 import mock
+from plumbum import local
 
+import pre_commit.constants as C
 from pre_commit.clientlib.validate_manifest import check_is_valid_manifest
 from pre_commit.clientlib.validate_manifest import InvalidManifestError
 from pre_commit.clientlib.validate_manifest import run
@@ -48,6 +50,18 @@ def test_returns_0_for_valid_manifest():
     assert ret == 0
 
 
+def test_uses_default_manifest_file_at_root_of_git(empty_git_dir):
+    local.path(C.MANIFEST_FILE).write("""
+hooks:
+    -
+        id: foo
+        name: Foo
+        entry: foo
+    """)
+    ret = run([])
+    assert ret == 0
+
+
 @pytest.mark.parametrize(('manifest', 'expected_exception_type'), (
     (
         """