Internal refactorings have been made in order to make the implementation of the
`pytest-subtests <https://github.com/pytest-dev/pytest-subtests>`__ plugin
possible, which adds unittest sub-test support and a new ``subtests`` fixture as discussed in
`#1367 <https://github.com/pytest-dev/pytest/issues/1367>`__.

For details on the internal refactorings, please see the details on the related PR.