Update pytest to 4.0.0

[pyup-bot]

This PR updates pytest from 3.10.1 to 4.0.0.

Changelog

4.0.0

=========================

Removals
--------

- `3737 <https://github.com/pytest-dev/pytest/issues/3737>`_: **RemovedInPytest4Warnings are now errors by default.**

Following our plan to remove deprecated features with as little disruption as
possible, all warnings of type ``RemovedInPytest4Warnings`` now generate errors
instead of warning messages.

**The affected features will be effectively removed in pytest 4.1**, so please consult the
`Deprecations and Removals <https://docs.pytest.org/en/latest/deprecations.html>`__
section in the docs for directions on how to update existing code.

In the pytest ``4.0.X`` series, it is possible to change the errors back into warnings as a stop
gap measure by adding this to your ``pytest.ini`` file:

.. code-block:: ini

   [pytest]
   filterwarnings =
       ignore::pytest.RemovedInPytest4Warning

But this will stop working when pytest ``4.1`` is released.

**If you have concerns** about the removal of a specific feature, please add a
comment to `4348 <https://github.com/pytest-dev/pytest/issues/4348>`__.


- `4358 <https://github.com/pytest-dev/pytest/issues/4358>`_: Remove the ``::()`` notation to denote a test class instance in node ids.

Previously, node ids that contain test instances would use ``::()`` to denote the instance like this::

   test_foo.py::Test::()::test_bar

The extra ``::()`` was puzzling to most users and has been removed, so that the test id becomes now::

   test_foo.py::Test::test_bar

This change could not accompany a deprecation period as is usual when user-facing functionality changes because
it was not really possible to detect when the functionality was being used explicitly.

The extra ``::()`` might have been removed in some places internally already,
which then led to confusion in places where it was expected, e.g. with
``--deselect`` (`4127 <https://github.com/pytest-dev/pytest/issues/4127>`_).

Test class instances are also not listed with ``--collect-only`` anymore.



Features
--------

- `4270 <https://github.com/pytest-dev/pytest/issues/4270>`_: The ``cache_dir`` option uses ``$TOX_ENV_DIR`` as prefix (if set in the environment).

This uses a different cache per tox environment by default.



Bug Fixes
---------

- `3554 <https://github.com/pytest-dev/pytest/issues/3554>`_: Fix ``CallInfo.__repr__`` for when the call is not finished yet.

Links

• PyPI: https://pypi.org/project/pytest
• Changelog: https://pyup.io/changelogs/pytest/
• Homepage: https://docs.pytest.org/en/latest/

[coveralls]

Coverage remained the same at 88.007% when pulling 4bd91f5 on pyup-update-pytest-3.10.1-to-4.0.0 into 1abdf7f on master.