Backport PR #8102: TEST: Add test for renaming files with checkpoint.

The checkpoint name should follow the file rename.

This catches a bug that I had in pgcontents where I was failing to properly rename checkpoints when files were renamed.  cf. https://github.com/ipython/ipython/issues/8101

IPython/html/services/contents/tests/test_contents_api.py

@@ -1,655 +1,687 b''
 # coding: utf-8
 """Test the contents webservice API."""
 
 import base64
 from contextlib import contextmanager
 import io
 import json
 import os
 import shutil
 from unicodedata import normalize
 
 pjoin = os.path.join
 
 import requests
 
 from ..filecheckpoints import GenericFileCheckpoints
 
 from IPython.config import Config
 from IPython.html.utils import url_path_join, url_escape, to_os_path
 from IPython.html.tests.launchnotebook import NotebookTestBase, assert_http_error
 from IPython.nbformat import read, write, from_dict
 from IPython.nbformat.v4 import (
     new_notebook, new_markdown_cell,
 )
 from IPython.nbformat import v2
 from IPython.utils import py3compat
 from IPython.utils.data import uniq_stable
 from IPython.utils.tempdir import TemporaryDirectory
 
 
 def notebooks_only(dir_model):
     return [nb for nb in dir_model['content'] if nb['type']=='notebook']
 
 def dirs_only(dir_model):
     return [x for x in dir_model['content'] if x['type']=='directory']
 
 
 class API(object):
     """Wrapper for contents API calls."""
     def __init__(self, base_url):
         self.base_url = base_url
 
     def _req(self, verb, path, body=None, params=None):
         response = requests.request(verb,
                 url_path_join(self.base_url, 'api/contents', path),
                 data=body, params=params,
         )
         response.raise_for_status()
         return response
 
     def list(self, path='/'):
         return self._req('GET', path)
 
     def read(self, path, type=None, format=None, content=None):
         params = {}
         if type is not None:
             params['type'] = type
         if format is not None:
             params['format'] = format
         if content == False:
             params['content'] = '0'
         return self._req('GET', path, params=params)
 
     def create_untitled(self, path='/', ext='.ipynb'):
         body = None
         if ext:
             body = json.dumps({'ext': ext})
         return self._req('POST', path, body)
 
     def mkdir_untitled(self, path='/'):
         return self._req('POST', path, json.dumps({'type': 'directory'}))
 
     def copy(self, copy_from, path='/'):
         body = json.dumps({'copy_from':copy_from})
         return self._req('POST', path, body)
 
     def create(self, path='/'):
         return self._req('PUT', path)
 
     def upload(self, path, body):
         return self._req('PUT', path, body)
 
     def mkdir(self, path='/'):
         return self._req('PUT', path, json.dumps({'type': 'directory'}))
 
     def copy_put(self, copy_from, path='/'):
         body = json.dumps({'copy_from':copy_from})
         return self._req('PUT', path, body)
 
     def save(self, path, body):
         return self._req('PUT', path, body)
 
     def delete(self, path='/'):
         return self._req('DELETE', path)
 
     def rename(self, path, new_path):
         body = json.dumps({'path': new_path})
         return self._req('PATCH', path, body)
 
     def get_checkpoints(self,  path):
         return self._req('GET', url_path_join(path, 'checkpoints'))
 
     def new_checkpoint(self,  path):
         return self._req('POST', url_path_join(path, 'checkpoints'))
 
     def restore_checkpoint(self, path, checkpoint_id):
         return self._req('POST', url_path_join(path, 'checkpoints', checkpoint_id))
 
     def delete_checkpoint(self, path, checkpoint_id):
         return self._req('DELETE', url_path_join(path, 'checkpoints', checkpoint_id))
 
 class APITest(NotebookTestBase):
     """Test the kernels web service API"""
     dirs_nbs = [('', 'inroot'),
                 ('Directory with spaces in', 'inspace'),
                 (u'unicodé', 'innonascii'),
                 ('foo', 'a'),
                 ('foo', 'b'),
                 ('foo', 'name with spaces'),
                 ('foo', u'unicodé'),
                 ('foo/bar', 'baz'),
                 ('ordering', 'A'),
                 ('ordering', 'b'),
                 ('ordering', 'C'),
                 (u'å b', u'ç d'),
                ]
     hidden_dirs = ['.hidden', '__pycache__']
 
     # Don't include root dir.
     dirs = uniq_stable([py3compat.cast_unicode(d) for (d,n) in dirs_nbs[1:]])
     top_level_dirs = {normalize('NFC', d.split('/')[0]) for d in dirs}
 
     @staticmethod
     def _blob_for_name(name):
         return name.encode('utf-8') + b'\xFF'
 
     @staticmethod
     def _txt_for_name(name):
         return u'%s text file' % name
     
     def to_os_path(self, api_path):
         return to_os_path(api_path, root=self.notebook_dir.name)
     
     def make_dir(self, api_path):
         """Create a directory at api_path"""
         os_path = self.to_os_path(api_path)
         try:
             os.makedirs(os_path)
         except OSError:
             print("Directory already exists: %r" % os_path)
 
     def make_txt(self, api_path, txt):
         """Make a text file at a given api_path"""
         os_path = self.to_os_path(api_path)
         with io.open(os_path, 'w', encoding='utf-8') as f:
             f.write(txt)
     
     def make_blob(self, api_path, blob):
         """Make a binary file at a given api_path"""
         os_path = self.to_os_path(api_path)
         with io.open(os_path, 'wb') as f:
             f.write(blob)
     
     def make_nb(self, api_path, nb):
         """Make a notebook file at a given api_path"""
         os_path = self.to_os_path(api_path)
         
         with io.open(os_path, 'w', encoding='utf-8') as f:
             write(nb, f, version=4)
 
     def delete_dir(self, api_path):
         """Delete a directory at api_path, removing any contents."""
         os_path = self.to_os_path(api_path)
         shutil.rmtree(os_path, ignore_errors=True)
 
     def delete_file(self, api_path):
         """Delete a file at the given path if it exists."""
         if self.isfile(api_path):
             os.unlink(self.to_os_path(api_path))
     
     def isfile(self, api_path):
         return os.path.isfile(self.to_os_path(api_path))
     
     def isdir(self, api_path):
         return os.path.isdir(self.to_os_path(api_path))
     
     def setUp(self):
 
         for d in (self.dirs + self.hidden_dirs):
             self.make_dir(d)
 
         for d, name in self.dirs_nbs:
             # create a notebook
             nb = new_notebook()
             self.make_nb(u'{}/{}.ipynb'.format(d, name), nb)
             
             # create a text file
             txt = self._txt_for_name(name)
             self.make_txt(u'{}/{}.txt'.format(d, name), txt)
             
             # create a binary file
             blob = self._blob_for_name(name)
             self.make_blob(u'{}/{}.blob'.format(d, name), blob)
 
         self.api = API(self.base_url())
 
     def tearDown(self):
         for dname in (list(self.top_level_dirs) + self.hidden_dirs):
             self.delete_dir(dname)
         self.delete_file('inroot.ipynb')
 
     def test_list_notebooks(self):
         nbs = notebooks_only(self.api.list().json())
         self.assertEqual(len(nbs), 1)
         self.assertEqual(nbs[0]['name'], 'inroot.ipynb')
 
         nbs = notebooks_only(self.api.list('/Directory with spaces in/').json())
         self.assertEqual(len(nbs), 1)
         self.assertEqual(nbs[0]['name'], 'inspace.ipynb')
 
         nbs = notebooks_only(self.api.list(u'/unicodé/').json())
         self.assertEqual(len(nbs), 1)
         self.assertEqual(nbs[0]['name'], 'innonascii.ipynb')
         self.assertEqual(nbs[0]['path'], u'unicodé/innonascii.ipynb')
 
         nbs = notebooks_only(self.api.list('/foo/bar/').json())
         self.assertEqual(len(nbs), 1)
         self.assertEqual(nbs[0]['name'], 'baz.ipynb')
         self.assertEqual(nbs[0]['path'], 'foo/bar/baz.ipynb')
 
         nbs = notebooks_only(self.api.list('foo').json())
         self.assertEqual(len(nbs), 4)
         nbnames = { normalize('NFC', n['name']) for n in nbs }
         expected = [ u'a.ipynb', u'b.ipynb', u'name with spaces.ipynb', u'unicodé.ipynb']
         expected = { normalize('NFC', name) for name in expected }
         self.assertEqual(nbnames, expected)
 
         nbs = notebooks_only(self.api.list('ordering').json())
         nbnames = [n['name'] for n in nbs]
         expected = ['A.ipynb', 'b.ipynb', 'C.ipynb']
         self.assertEqual(nbnames, expected)
 
     def test_list_dirs(self):
         dirs = dirs_only(self.api.list().json())
         dir_names = {normalize('NFC', d['name']) for d in dirs}
         self.assertEqual(dir_names, self.top_level_dirs)  # Excluding hidden dirs
 
     def test_get_dir_no_content(self):
         for d in self.dirs:
             model = self.api.read(d, content=False).json()
             self.assertEqual(model['path'], d)
             self.assertEqual(model['type'], 'directory')
             self.assertIn('content', model)
             self.assertEqual(model['content'], None)
 
     def test_list_nonexistant_dir(self):
         with assert_http_error(404):
             self.api.list('nonexistant')
 
     def test_get_nb_contents(self):
         for d, name in self.dirs_nbs:
             path = url_path_join(d, name + '.ipynb')
             nb = self.api.read(path).json()
             self.assertEqual(nb['name'], u'%s.ipynb' % name)
             self.assertEqual(nb['path'], path)
             self.assertEqual(nb['type'], 'notebook')
             self.assertIn('content', nb)
             self.assertEqual(nb['format'], 'json')
             self.assertIn('metadata', nb['content'])
             self.assertIsInstance(nb['content']['metadata'], dict)
 
     def test_get_nb_no_content(self):
         for d, name in self.dirs_nbs:
             path = url_path_join(d, name + '.ipynb')
             nb = self.api.read(path, content=False).json()
             self.assertEqual(nb['name'], u'%s.ipynb' % name)
             self.assertEqual(nb['path'], path)
             self.assertEqual(nb['type'], 'notebook')
             self.assertIn('content', nb)
             self.assertEqual(nb['content'], None)
 
     def test_get_contents_no_such_file(self):
         # Name that doesn't exist - should be a 404
         with assert_http_error(404):
             self.api.read('foo/q.ipynb')
 
     def test_get_text_file_contents(self):
         for d, name in self.dirs_nbs:
             path = url_path_join(d, name + '.txt')
             model = self.api.read(path).json()
             self.assertEqual(model['name'], u'%s.txt' % name)
             self.assertEqual(model['path'], path)
             self.assertIn('content', model)
             self.assertEqual(model['format'], 'text')
             self.assertEqual(model['type'], 'file')
             self.assertEqual(model['content'], self._txt_for_name(name))
 
         # Name that doesn't exist - should be a 404
         with assert_http_error(404):
             self.api.read('foo/q.txt')
 
         # Specifying format=text should fail on a non-UTF-8 file
         with assert_http_error(400):
             self.api.read('foo/bar/baz.blob', type='file', format='text')
 
     def test_get_binary_file_contents(self):
         for d, name in self.dirs_nbs:
             path = url_path_join(d, name + '.blob')
             model = self.api.read(path).json()
             self.assertEqual(model['name'], u'%s.blob' % name)
             self.assertEqual(model['path'], path)
             self.assertIn('content', model)
             self.assertEqual(model['format'], 'base64')
             self.assertEqual(model['type'], 'file')
             self.assertEqual(
                 base64.decodestring(model['content'].encode('ascii')),
                 self._blob_for_name(name),
             )
 
         # Name that doesn't exist - should be a 404
         with assert_http_error(404):
             self.api.read('foo/q.txt')
 
     def test_get_bad_type(self):
         with assert_http_error(400):
             self.api.read(u'unicodé', type='file')  # this is a directory
 
         with assert_http_error(400):
             self.api.read(u'unicodé/innonascii.ipynb', type='directory')
 
     def _check_created(self, resp, path, type='notebook'):
         self.assertEqual(resp.status_code, 201)
         location_header = py3compat.str_to_unicode(resp.headers['Location'])
         self.assertEqual(location_header, url_escape(url_path_join(u'/api/contents', path)))
         rjson = resp.json()
         self.assertEqual(rjson['name'], path.rsplit('/', 1)[-1])
         self.assertEqual(rjson['path'], path)
         self.assertEqual(rjson['type'], type)
         isright = self.isdir if type == 'directory' else self.isfile
         assert isright(path)
 
     def test_create_untitled(self):
         resp = self.api.create_untitled(path=u'å b')
         self._check_created(resp, u'å b/Untitled.ipynb')
 
         # Second time
         resp = self.api.create_untitled(path=u'å b')
         self._check_created(resp, u'å b/Untitled1.ipynb')
 
         # And two directories down
         resp = self.api.create_untitled(path='foo/bar')
         self._check_created(resp, 'foo/bar/Untitled.ipynb')
 
     def test_create_untitled_txt(self):
         resp = self.api.create_untitled(path='foo/bar', ext='.txt')
         self._check_created(resp, 'foo/bar/untitled.txt', type='file')
 
         resp = self.api.read(path='foo/bar/untitled.txt')
         model = resp.json()
         self.assertEqual(model['type'], 'file')
         self.assertEqual(model['format'], 'text')
         self.assertEqual(model['content'], '')
 
     def test_upload(self):
         nb = new_notebook()
         nbmodel = {'content': nb, 'type': 'notebook'}
         path = u'å b/Upload tést.ipynb'
         resp = self.api.upload(path, body=json.dumps(nbmodel))
         self._check_created(resp, path)
 
     def test_mkdir_untitled(self):
         resp = self.api.mkdir_untitled(path=u'å b')
         self._check_created(resp, u'å b/Untitled Folder', type='directory')
 
         # Second time
         resp = self.api.mkdir_untitled(path=u'å b')
         self._check_created(resp, u'å b/Untitled Folder 1', type='directory')
 
         # And two directories down
         resp = self.api.mkdir_untitled(path='foo/bar')
         self._check_created(resp, 'foo/bar/Untitled Folder', type='directory')
 
     def test_mkdir(self):
         path = u'å b/New ∂ir'
         resp = self.api.mkdir(path)
         self._check_created(resp, path, type='directory')
 
     def test_mkdir_hidden_400(self):
         with assert_http_error(400):
             resp = self.api.mkdir(u'å b/.hidden')
 
     def test_upload_txt(self):
         body = u'ünicode téxt'
         model = {
             'content' : body,
             'format'  : 'text',
             'type'    : 'file',
         }
         path = u'å b/Upload tést.txt'
         resp = self.api.upload(path, body=json.dumps(model))
 
         # check roundtrip
         resp = self.api.read(path)
         model = resp.json()
         self.assertEqual(model['type'], 'file')
         self.assertEqual(model['format'], 'text')
         self.assertEqual(model['content'], body)
 
     def test_upload_b64(self):
         body = b'\xFFblob'
         b64body = base64.encodestring(body).decode('ascii')
         model = {
             'content' : b64body,
             'format'  : 'base64',
             'type'    : 'file',
         }
         path = u'å b/Upload tést.blob'
         resp = self.api.upload(path, body=json.dumps(model))
 
         # check roundtrip
         resp = self.api.read(path)
         model = resp.json()
         self.assertEqual(model['type'], 'file')
         self.assertEqual(model['path'], path)
         self.assertEqual(model['format'], 'base64')
         decoded = base64.decodestring(model['content'].encode('ascii'))
         self.assertEqual(decoded, body)
 
     def test_upload_v2(self):
         nb = v2.new_notebook()
         ws = v2.new_worksheet()
         nb.worksheets.append(ws)
         ws.cells.append(v2.new_code_cell(input='print("hi")'))
         nbmodel = {'content': nb, 'type': 'notebook'}
         path = u'å b/Upload tést.ipynb'
         resp = self.api.upload(path, body=json.dumps(nbmodel))
         self._check_created(resp, path)
         resp = self.api.read(path)
         data = resp.json()
         self.assertEqual(data['content']['nbformat'], 4)
 
     def test_copy(self):
         resp = self.api.copy(u'å b/ç d.ipynb', u'å b')
         self._check_created(resp, u'å b/ç d-Copy1.ipynb')
         
         resp = self.api.copy(u'å b/ç d.ipynb', u'å b')
         self._check_created(resp, u'å b/ç d-Copy2.ipynb')
     
     def test_copy_copy(self):
         resp = self.api.copy(u'å b/ç d.ipynb', u'å b')
         self._check_created(resp, u'å b/ç d-Copy1.ipynb')
         
         resp = self.api.copy(u'å b/ç d-Copy1.ipynb', u'å b')
         self._check_created(resp, u'å b/ç d-Copy2.ipynb')
     
     def test_copy_path(self):
         resp = self.api.copy(u'foo/a.ipynb', u'å b')
         self._check_created(resp, u'å b/a.ipynb')
         
         resp = self.api.copy(u'foo/a.ipynb', u'å b')
         self._check_created(resp, u'å b/a-Copy1.ipynb')
 
     def test_copy_put_400(self):
         with assert_http_error(400):
             resp = self.api.copy_put(u'å b/ç d.ipynb', u'å b/cøpy.ipynb')
 
     def test_copy_dir_400(self):
         # can't copy directories
         with assert_http_error(400):
             resp = self.api.copy(u'å b', u'foo')
 
     def test_delete(self):
         for d, name in self.dirs_nbs:
             print('%r, %r' % (d, name))
             resp = self.api.delete(url_path_join(d, name + '.ipynb'))
             self.assertEqual(resp.status_code, 204)
 
         for d in self.dirs + ['/']:
             nbs = notebooks_only(self.api.list(d).json())
             print('------')
             print(d)
             print(nbs)
             self.assertEqual(nbs, [])
 
     def test_delete_dirs(self):
         # depth-first delete everything, so we don't try to delete empty directories
         for name in sorted(self.dirs + ['/'], key=len, reverse=True):
             listing = self.api.list(name).json()['content']
             for model in listing:
                 self.api.delete(model['path'])
         listing = self.api.list('/').json()['content']
         self.assertEqual(listing, [])
 
     def test_delete_non_empty_dir(self):
         """delete non-empty dir raises 400"""
         with assert_http_error(400):
             self.api.delete(u'å b')
 
     def test_rename(self):
         resp = self.api.rename('foo/a.ipynb', 'foo/z.ipynb')
         self.assertEqual(resp.headers['Location'].split('/')[-1], 'z.ipynb')
         self.assertEqual(resp.json()['name'], 'z.ipynb')
         self.assertEqual(resp.json()['path'], 'foo/z.ipynb')
         assert self.isfile('foo/z.ipynb')
 
         nbs = notebooks_only(self.api.list('foo').json())
         nbnames = set(n['name'] for n in nbs)
         self.assertIn('z.ipynb', nbnames)
         self.assertNotIn('a.ipynb', nbnames)
 
+    def test_checkpoints_follow_file(self):
+
+        # Read initial file state
+        orig = self.api.read('foo/a.ipynb')
+
+        # Create a checkpoint of initial state
+        r = self.api.new_checkpoint('foo/a.ipynb')
+        cp1 = r.json()
+
+        # Modify file and save
+        nbcontent = json.loads(orig.text)['content']
+        nb = from_dict(nbcontent)
+        hcell = new_markdown_cell('Created by test')
+        nb.cells.append(hcell)
+        nbmodel = {'content': nb, 'type': 'notebook'}
+        self.api.save('foo/a.ipynb', body=json.dumps(nbmodel))
+
+        # Rename the file.
+        self.api.rename('foo/a.ipynb', 'foo/z.ipynb')
+
+        # Looking for checkpoints in the old location should yield no results.
+        self.assertEqual(self.api.get_checkpoints('foo/a.ipynb').json(), [])
+
+        # Looking for checkpoints in the new location should work.
+        cps = self.api.get_checkpoints('foo/z.ipynb').json()
+        self.assertEqual(cps, [cp1])
+
+        # Delete the file.  The checkpoint should be deleted as well.
+        self.api.delete('foo/z.ipynb')
+        cps = self.api.get_checkpoints('foo/z.ipynb').json()
+        self.assertEqual(cps, [])
+
     def test_rename_existing(self):
         with assert_http_error(409):
             self.api.rename('foo/a.ipynb', 'foo/b.ipynb')
 
     def test_save(self):
         resp = self.api.read('foo/a.ipynb')
         nbcontent = json.loads(resp.text)['content']
         nb = from_dict(nbcontent)
         nb.cells.append(new_markdown_cell(u'Created by test ³'))
 
         nbmodel= {'content': nb, 'type': 'notebook'}
         resp = self.api.save('foo/a.ipynb', body=json.dumps(nbmodel))
 
         nbcontent = self.api.read('foo/a.ipynb').json()['content']
         newnb = from_dict(nbcontent)
         self.assertEqual(newnb.cells[0].source,
                          u'Created by test ³')
 
     def test_checkpoints(self):
         resp = self.api.read('foo/a.ipynb')
         r = self.api.new_checkpoint('foo/a.ipynb')
         self.assertEqual(r.status_code, 201)
         cp1 = r.json()
         self.assertEqual(set(cp1), {'id', 'last_modified'})
         self.assertEqual(r.headers['Location'].split('/')[-1], cp1['id'])
 
         # Modify it
         nbcontent = json.loads(resp.text)['content']
         nb = from_dict(nbcontent)
         hcell = new_markdown_cell('Created by test')
         nb.cells.append(hcell)
         # Save
         nbmodel= {'content': nb, 'type': 'notebook'}
         resp = self.api.save('foo/a.ipynb', body=json.dumps(nbmodel))
 
         # List checkpoints
         cps = self.api.get_checkpoints('foo/a.ipynb').json()
         self.assertEqual(cps, [cp1])
 
         nbcontent = self.api.read('foo/a.ipynb').json()['content']
         nb = from_dict(nbcontent)
         self.assertEqual(nb.cells[0].source, 'Created by test')
 
         # Restore cp1
         r = self.api.restore_checkpoint('foo/a.ipynb', cp1['id'])
         self.assertEqual(r.status_code, 204)
         nbcontent = self.api.read('foo/a.ipynb').json()['content']
         nb = from_dict(nbcontent)
         self.assertEqual(nb.cells, [])
 
         # Delete cp1
         r = self.api.delete_checkpoint('foo/a.ipynb', cp1['id'])
         self.assertEqual(r.status_code, 204)
         cps = self.api.get_checkpoints('foo/a.ipynb').json()
         self.assertEqual(cps, [])
 
     def test_file_checkpoints(self):
         """
         Test checkpointing of non-notebook files.
         """
         filename = 'foo/a.txt'
         resp = self.api.read(filename)
         orig_content = json.loads(resp.text)['content']
 
         # Create a checkpoint.
         r = self.api.new_checkpoint(filename)
         self.assertEqual(r.status_code, 201)
         cp1 = r.json()
         self.assertEqual(set(cp1), {'id', 'last_modified'})
         self.assertEqual(r.headers['Location'].split('/')[-1], cp1['id'])
 
         # Modify the file and save.
         new_content = orig_content + '\nsecond line'
         model = {
             'content': new_content,
             'type': 'file',
             'format': 'text',
         }
         resp = self.api.save(filename, body=json.dumps(model))
 
         # List checkpoints
         cps = self.api.get_checkpoints(filename).json()
         self.assertEqual(cps, [cp1])
 
         content = self.api.read(filename).json()['content']
         self.assertEqual(content, new_content)
 
         # Restore cp1
         r = self.api.restore_checkpoint(filename, cp1['id'])
         self.assertEqual(r.status_code, 204)
         restored_content = self.api.read(filename).json()['content']
         self.assertEqual(restored_content, orig_content)
 
         # Delete cp1
         r = self.api.delete_checkpoint(filename, cp1['id'])
         self.assertEqual(r.status_code, 204)
         cps = self.api.get_checkpoints(filename).json()
         self.assertEqual(cps, [])
 
     @contextmanager
     def patch_cp_root(self, dirname):
         """
         Temporarily patch the root dir of our checkpoint manager.
         """
         cpm = self.notebook.contents_manager.checkpoints
         old_dirname = cpm.root_dir
         cpm.root_dir = dirname
         try:
             yield
         finally:
             cpm.root_dir = old_dirname
 
     def test_checkpoints_separate_root(self):
         """
         Test that FileCheckpoints functions correctly even when it's
         using a different root dir from FileContentsManager.  This also keeps
         the implementation honest for use with ContentsManagers that don't map
         models to the filesystem
 
         Override this method to a no-op when testing other managers.
         """
         with TemporaryDirectory() as td:
             with self.patch_cp_root(td):
                 self.test_checkpoints()
 
         with TemporaryDirectory() as td:
             with self.patch_cp_root(td):
                 self.test_file_checkpoints()
 
 
 class GenericFileCheckpointsAPITest(APITest):
     """
     Run the tests from APITest with GenericFileCheckpoints.
     """
     config = Config()
     config.FileContentsManager.checkpoints_class = GenericFileCheckpoints
 
     def test_config_did_something(self):
 
         self.assertIsInstance(
             self.notebook.contents_manager.checkpoints,
             GenericFileCheckpoints,
         )