Fix autoupdate spamming with defaults.

tests/jsonschema_extensions_test.py

@@ -1,5 +1,6 @@
 
 from pre_commit.jsonschema_extensions import apply_defaults
+from pre_commit.jsonschema_extensions import remove_defaults
 
 
 def test_apply_defaults_copies_object():
@@ -56,3 +57,25 @@ def test_apply_defaults_copies():
     ret1 = apply_defaults({}, schema)
     ret2 = apply_defaults({}, schema)
     assert ret1['foo'] is not ret2['foo']
+
+
+def test_remove_defaults_copies_object():
+    input = {}
+    ret = remove_defaults(input, {})
+    assert ret is not input
+
+
+def test_remove_defaults_does_not_remove_non_default():
+    ret = remove_defaults(
+        {'foo': 'bar'},
+        {'properties': {'foo': {'default': 'baz'}}},
+    )
+    assert ret == {'foo': 'bar'}
+
+
+def test_remove_defaults_removes_default():
+    ret = remove_defaults(
+        {'foo': 'bar'},
+        {'properties': {'foo': {'default': 'bar'}}},
+    )
+    assert ret == {}