- Issue #17467: add readline and readlines support to mock_open in
  unittest.mock.

- Issue #17015: When it has a spec, a Mock object now inspects its signature
  when matching calls, so that arguments can be matched positionally or
  by name.

- Issue #15323: improve failure message of Mock.assert_called_once_with

- Issue #14857: fix regression in references to PEP 3135 implicit __class__
  closure variable (Reopens issue #12370)

- Issue #14295: Add unittest.mock