Release 2.5.0

This commit prepares the NEWS file for the 2.5.0 release.

testtools.compat: provide BytesIO, StringIO again

Fix tests with Python 3.10

Note Python 3.5 is EOL and will be dropped after the next release

This allows projects dependent on testtools.compat some respite if
they haven't been updated for python 3.10 yet.

Add support for Python 3.9

Fix setuptools warnings

Fix UserWarning: Usage of dash-separated ... will not be supported in future versions. Please use the underscore name ... instead

In Python 3, error messages have become a bit more precise. For
instance, the following code snippet:

----
class Foo():
    def bar(self, a):
        pass

try:
    Foo().bar(1, 2)
except TypeError as e:
    print(e)
----

will return:

- in Python 3.9: "bar() takes 2 positional arguments but 3 were given"
- in Python 3.10: "Foo.bar() takes 2 positional arguments but 3 were
  given"

Fix our tests accordingly.

Publicly expose the SameMembers matcher

Reduce dependencies

We can do this ourselves quite easily.

Signed-off-by: Stephen Finucane <stephen@that.guru>

This is kept separately from the reintroduction of 'try_imports' to keep
that patch reasonable.

Signed-off-by: Stephen Finucane <stephen@that.guru>

There are few if any people still (knowingly) using the 'extras' lib.
OpenStack users have their own implementation (sigh) in 'oslo.utils' and
everyone else is getting by with try-except statements. Reintroduce this
utility to 'testtools.helpers', allowing us to eventually drop the
dependency on extras. Note however that we can't actually do this yet
since 'fixtures' has an implicit dependency on 'extras' through
'testtools', and we break that by removing it here.

Signed-off-by: Stephen Finucane <stephen@that.guru>

This was being used in places to handle differences between Python 2 and
Python 3. Since we only care about the latter now, the utility can be
removed.

Signed-off-by: Stephen Finucane <stephen@that.guru>

We also need to override the install command or VIRTUAL_ENV environment
variable.

Signed-off-by: Stephen Finucane <stephen@that.guru>

This was used to workaround some issues with 'hasattr' on Python 2.x
versions, discussed in the source for extras (where this utility was
moved to make it more useful to others) [1] and elsewhere on the
internet [2]. These issues are no longer present on the versions of
Python we now support (Python 3.6+) so this is no longer necessary.

[1] https://github.com/testing-cabal/extras/blob/1.0.0/extras/__init__.py#L101-L108
[2] https://hynek.me/articles/hasattr/



Signed-off-by: Stephen Finucane <stephen@that.guru>

Signed-off-by: Stephen Finucane <stephen@that.guru>

Remove unittest2 usage from testtools

Resolve DeprecationWarnings under python 36

Fix github actions