pytest will just import the files passed to it and try to run tests.
Since we need to run some setup code convert the tests directory to
a Python package and do the initialization in __init__.py. This makes
the init code (env vars, typelib search path, dbus) always run when
something from the package gets imported.

    python3 setup.py build_tests  # build pygobject and tests
    py.test-3 tests/test_gi.py  # run tests in test_gi.py only

Set the versions in runtests.py instead of repeating it in every
test module.

Add a new TEST_GTK_VERSION env var which defaults to "3.0".
Allows to run tests with gtk4 using "make check TEST_GTK_VERSION=4.0"

gi tries to import the latest version of typelibs which can cause
existing code to break when a newer typelib is released.
Emit an ImportWarning when gi.require_version() is not used to give
developers this awareness so they can future proof their code.

https://bugzilla.gnome.org/show_bug.cgi?id=727379

Remove the override for Pango.Context and the get_metrics method. This can
be done now that tail end method arguments with "allow-none" are implicitly
defaulted to use None/NULL.

Strip trailing underscore from module level items before
calling g_irepository_find_by_name. This fixes a problem
with GI module level items having the same name as a Python
keyword raising an AttributeError during access (Pango.break_).

https://bugzilla.gnome.org/show_bug.cgi?id=697363

Split the huge test_overrides.py into separate files for gdk, gtk, gio, glib,
and pango. Further split the monolithic classes for Gtk and Gio into several
ones.

https://bugzilla.gnome.org/show_bug.cgi?id=683188