Hi ccokeke 
If I use URL directly, it supposedly works.
Also, response code will be 301
    
```
def test_create_snapshot_post_invalid_metadata(self):
        share = test_data.share
        url = '/project/share_snapshots/something/share_snapshot_create'
        formData = {
            'name': 'new_snapshot',
            'description': 'This is test snapshot',
            'method': 'CreateForm',
            'size': 1,
            'type': 'NFS',
            'metadata': 'foo',
            'share_id': share.id,
        }

        self.mock_object(
            api_manila,
            "share_snapshot_create",
            mock.Mock(side_effect=ValidationError(
                'Expected only pairs of key=value.'
            ))
        )
        res = self.client.post(url, formData)
        self.assertEqual(res.status_code, 301)
        self.assertFalse(api_manila.share_snapshot_create.called)
```