Remove 3.5 and xenial support (SC-711) (#1167)

Includes:
 - Update tox.ini and .travis.yml accordingly
 - Cleanup tox.ini with new tox syntax and cloud-init dependencies
 - Update documentation accordingly
 - Replace/remove xenial references where additional testing isn't required
 - Remove xenial checks in integration tests
 - Replace yield_fixture with fixture in pytest tests

Sections of code commented with lines like "Remove when Xenial is no
longer supported" still exist as they're require additional testing.

26 files changed, 137 insertions, 237 deletions

diff --git a/.travis.yml b/.travis.yml
index 2351246b..208bed23 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -75,17 +75,17 @@ matrix:
             - cp /usr/share/doc/sbuild/examples/example.sbuildrc /home/$USER/.sbuildrc
           script:
             # Ubuntu LTS: Build
-            - ./packages/bddeb -S -d --release xenial
+            - ./packages/bddeb -S -d --release bionic
             - |
                 needs_caching=false
-                if [ -e "$TRAVIS_BUILD_DIR/chroots/xenial-amd64.tar" ]; then
+                if [ -e "$TRAVIS_BUILD_DIR/chroots/bionic-amd64.tar" ]; then
                     # If we have a cached chroot, move it into place
-                    sudo mkdir -p /var/lib/schroot/chroots/xenial-amd64
-                    sudo tar --sparse --xattrs --preserve-permissions --numeric-owner -xf "$TRAVIS_BUILD_DIR/chroots/xenial-amd64.tar" -C /var/lib/schroot/chroots/xenial-amd64
+                    sudo mkdir -p /var/lib/schroot/chroots/bionic-amd64
+                    sudo tar --sparse --xattrs --preserve-permissions --numeric-owner -xf "$TRAVIS_BUILD_DIR/chroots/bionic-amd64.tar" -C /var/lib/schroot/chroots/bionic-amd64
                     # Write its configuration
-                    cat > sbuild-xenial-amd64 << EOM
-                [xenial-amd64]
-                description=xenial-amd64
+                    cat > sbuild-bionic-amd64 << EOM
+                [bionic-amd64]
+                description=bionic-amd64
                 groups=sbuild,root,admin
                 root-groups=sbuild,root,admin
                 # Uncomment these lines to allow members of these groups to access
@@ -95,20 +95,20 @@ matrix:
                 type=directory
                 profile=sbuild
                 union-type=overlay
-                directory=/var/lib/schroot/chroots/xenial-amd64
+                directory=/var/lib/schroot/chroots/bionic-amd64
                 EOM
-                    sudo mv sbuild-xenial-amd64 /etc/schroot/chroot.d/
-                    sudo chown root /etc/schroot/chroot.d/sbuild-xenial-amd64
+                    sudo mv sbuild-bionic-amd64 /etc/schroot/chroot.d/
+                    sudo chown root /etc/schroot/chroot.d/sbuild-bionic-amd64
                     # And ensure it's up-to-date.
-                    before_pkgs="$(sudo schroot -c source:xenial-amd64 -d / dpkg -l | sha256sum)"
-                    sudo schroot -c source:xenial-amd64 -d / -- sh -c "apt-get update && apt-get -qqy upgrade"
-                    after_pkgs=$(sudo schroot -c source:xenial-amd64 -d / dpkg -l | sha256sum)
+                    before_pkgs="$(sudo schroot -c source:bionic-amd64 -d / dpkg -l | sha256sum)"
+                    sudo schroot -c source:bionic-amd64 -d / -- sh -c "apt-get update && apt-get -qqy upgrade"
+                    after_pkgs=$(sudo schroot -c source:bionic-amd64 -d / dpkg -l | sha256sum)
                     if [ "$before_pkgs" != "$after_pkgs" ]; then
                         needs_caching=true
                     fi
                 else
                     # Otherwise, create the chroot
-                    sudo -E su $USER -c 'mk-sbuild xenial'
+                    sudo -E su $USER -c 'mk-sbuild bionic'
                     needs_caching=true
                 fi
                 # If there are changes to the schroot (or it's entirely new),
@@ -116,19 +116,19 @@ matrix:
                 # move it into the cached dir; no need to compress it because
                 # Travis will do that anyway
                 if [ "$needs_caching" = "true" ]; then
-                    sudo tar --sparse --xattrs --xattrs-include=* -cf "$TRAVIS_BUILD_DIR/chroots/xenial-amd64.tar" -C /var/lib/schroot/chroots/xenial-amd64 .
+                    sudo tar --sparse --xattrs --xattrs-include=* -cf "$TRAVIS_BUILD_DIR/chroots/bionic-amd64.tar" -C /var/lib/schroot/chroots/bionic-amd64 .
                 fi
             # Use sudo to get a new shell where we're in the sbuild group
             # Don't run integration tests when build fails
             - |
-                sudo -E su $USER -c 'DEB_BUILD_OPTIONS=nocheck sbuild --nolog --no-run-lintian --no-run-autopkgtest --verbose --dist=xenial cloud-init_*.dsc' &&
+                sudo -E su $USER -c 'DEB_BUILD_OPTIONS=nocheck sbuild --nolog --no-run-lintian --no-run-autopkgtest --verbose --dist=bionic cloud-init_*.dsc' &&
                   ssh-keygen -P "" -q -f ~/.ssh/id_rsa                                                         &&
                   sg lxd -c 'CLOUD_INIT_CLOUD_INIT_SOURCE="$(ls *.deb)" tox -e integration-tests-ci'
-        - python: 3.5
+        - python: 3.6
           env:
-              TOXENV=xenial
-              PYTEST_ADDOPTS=-v  # List all tests run by pytest
-          dist: xenial
+            TOXENV=lowest-supported
+            PYTEST_ADDOPTS=-v  # List all tests run by pytest
+          dist: bionic
         - python: 3.6
           env: TOXENV=flake8
         - python: 3.6
@@ -145,4 +145,3 @@ matrix:
         - python: 3.9
         - python: 3.8
         - python: 3.7
-        - python: 3.5
diff --git a/cloudinit/config/cc_apt_configure.py b/cloudinit/config/cc_apt_configure.py
index b0728517..37077a9f 100644
--- a/cloudinit/config/cc_apt_configure.py
+++ b/cloudinit/config/cc_apt_configure.py
@@ -133,7 +133,7 @@ meta = {
               source1:
                   keyid: 'keyid'
                   keyserver: 'keyserverurl'
-                  source: 'deb [signed-by=$KEY_FILE] http://<url>/ xenial main'
+                  source: 'deb [signed-by=$KEY_FILE] http://<url>/ bionic main'
               source2:
                   source: 'ppa:<ppa-name>'
               source3:
diff --git a/cloudinit/distros/debian.py b/cloudinit/distros/debian.py
index 0105a383..9effa0a0 100644
--- a/cloudinit/distros/debian.py
+++ b/cloudinit/distros/debian.py
@@ -257,7 +257,7 @@ class Distro(distros.Distro):
             pkgs = []
 
         e = os.environ.copy()
-        # See: http://manpages.ubuntu.com/manpages/xenial/man7/debconf.7.html
+        # See: http://manpages.ubuntu.com/manpages/bionic/man7/debconf.7.html
         e["DEBIAN_FRONTEND"] = "noninteractive"
 
         wcfg = self.get_option("apt_get_wrapper", APT_GET_WRAPPER)
diff --git a/conftest.py b/conftest.py
index ffcb3233..3979eb0a 100644
--- a/conftest.py
+++ b/conftest.py
@@ -65,7 +65,7 @@ class _FixtureUtils:
         return result[0]
 
 
-@pytest.yield_fixture(autouse=True)
+@pytest.fixture(autouse=True)
 def disable_subp_usage(request, fixture_utils):
     """
     Across all (pytest) tests, ensure that subp.subp is not invoked.
@@ -166,7 +166,7 @@ def fixture_utils():
     return _FixtureUtils
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def httpretty():
     """
     Enable HTTPretty for duration of the testcase, resetting before and after.
diff --git a/doc/examples/cloud-config-apt.txt b/doc/examples/cloud-config-apt.txt
index 778187b5..39f546e1 100644
--- a/doc/examples/cloud-config-apt.txt
+++ b/doc/examples/cloud-config-apt.txt
@@ -254,7 +254,7 @@ apt:
       #
       # Creates a file in /etc/apt/sources.list.d/ for the sources list entry
       # based on the key: "/etc/apt/sources.list.d/curtin-dev-ppa.list"
-      source: "deb http://ppa.launchpad.net/curtin-dev/test-archive/ubuntu xenial main"
+      source: "deb http://ppa.launchpad.net/curtin-dev/test-archive/ubuntu bionic main"
 
       # 2.2 keyid
       #
@@ -282,13 +282,13 @@ apt:
       # They will be replaced with the default or specified mirrors and the
       # running release.
       # The entry below would be possibly turned into:
-      #   source: deb http://archive.ubuntu.com/ubuntu xenial multiverse
+      #   source: deb http://archive.ubuntu.com/ubuntu bionic multiverse
       source: deb [signed-by=$KEY_FILE] $MIRROR $RELEASE multiverse
       keyid: F430BBA5
 
     my-repo3.list:
       # this would have the same end effect as 'ppa:curtin-dev/test-archive'
-      source: "deb http://ppa.launchpad.net/curtin-dev/test-archive/ubuntu xenial main"
+      source: "deb http://ppa.launchpad.net/curtin-dev/test-archive/ubuntu bionic main"
       keyid: F430BBA5 # GPG key ID published on the key server
       filename: curtin-dev-ppa.list
 
diff --git a/doc/examples/cloud-config-chef.txt b/doc/examples/cloud-config-chef.txt
index 414111a1..9bb3c150 100644
--- a/doc/examples/cloud-config-chef.txt
+++ b/doc/examples/cloud-config-chef.txt
@@ -4,9 +4,6 @@
 # list of recipes when the instance boots for the first time.
 # Make sure that this file is valid yaml before starting instances.
 # It should be passed as user-data when starting the instance.
-#
-# This example assumes the instance is 16.04 (xenial)
-
 
 # The default is to install from packages.
 
@@ -55,7 +52,7 @@ chef:
 
   # Valid values are 'accept' and 'accept-no-persist'
   chef_license: "accept"
-  
+
   # Valid values are 'gems' and 'packages' and 'omnibus'
   install_type: "packages"
 
diff --git a/doc/rtd/topics/debugging.rst b/doc/rtd/topics/debugging.rst
index b897a318..a4a2779f 100644
--- a/doc/rtd/topics/debugging.rst
+++ b/doc/rtd/topics/debugging.rst
@@ -88,7 +88,7 @@ To quickly obtain a cloud-init log try using lxc on any ubuntu system:
 
 .. code-block:: shell-session
 
-    $ lxc init ubuntu-daily:xenial x1
+    $ lxc init ubuntu-daily:focal x1
     $ lxc start x1
     $ # Take lxc's cloud-init.log and pipe it to the analyzer
     $ lxc file pull x1/var/log/cloud-init.log - | cloud-init analyze dump -i -
@@ -104,13 +104,13 @@ To quickly analyze a KVM a cloud-init log:
 
 .. code-block:: shell-session
 
-    $ wget https://cloud-images.ubuntu.com/daily/server/xenial/current/xenial-server-cloudimg-amd64.img
+    $ wget https://cloud-images.ubuntu.com/daily/server/focal/current/focal-server-cloudimg-amd64.img
 
 2. Create a snapshot image to preserve the original cloud-image
 
 .. code-block:: shell-session
 
-    $ qemu-img create -b xenial-server-cloudimg-amd64.img -f qcow2 \
+    $ qemu-img create -b focal-server-cloudimg-amd64.img -f qcow2 \
     test-cloudinit.qcow2
 
 3. Create a seed image with metadata using `cloud-localds`
diff --git a/doc/rtd/topics/testing.rst b/doc/rtd/topics/testing.rst
index 7a1e3eec..5543c6f5 100644
--- a/doc/rtd/topics/testing.rst
+++ b/doc/rtd/topics/testing.rst
@@ -54,28 +54,22 @@ Test Layout
 * pytest tests should use bare ``assert`` statements, to take advantage
   of pytest's `assertion introspection`_
 
-  * For ``==`` and other commutative assertions, the expected value
-    should be placed before the value under test:
-    ``assert expected_value == function_under_test()``
-
-
 ``pytest`` Version Gotchas
 --------------------------
 
-As we still support Ubuntu 16.04 (Xenial Xerus), we can only use pytest
-features that are available in v2.8.7.  This is an inexhaustive list of
+As we still support Ubuntu 18.04 (Bionic Beaver), we can only use pytest
+features that are available in v3.3.2.  This is an inexhaustive list of
 ways in which this may catch you out:
 
-* Support for using ``yield`` in ``pytest.fixture`` functions was only
-  introduced in `pytest 3.0`_.  Such functions must instead use the
-  ``pytest.yield_fixture`` decorator.
-
 * Only the following built-in fixtures are available [#fixture-list]_:
 
   * ``cache``
   * ``capfd``
-  * ``caplog`` (provided by ``python3-pytest-catchlog`` on xenial)
+  * ``capfdbinary``
+  * ``caplog``
   * ``capsys``
+  * ``capsysbinary``
+  * ``doctest_namespace``
   * ``monkeypatch``
   * ``pytestconfig``
   * ``record_xml_property``
@@ -83,22 +77,6 @@ ways in which this may catch you out:
   * ``tmpdir_factory``
   * ``tmpdir``
 
-* On xenial, the objects returned by the ``tmpdir`` fixture cannot be
-  used where paths are required; they are rejected as invalid paths.
-  You must instead use their ``.strpath`` attribute.
-
-  * For example, instead of ``util.write_file(tmpdir.join("some_file"),
-    ...)``, you should write
-    ``util.write_file(tmpdir.join("some_file").strpath, ...)``.
-
-* The `pytest.param`_ function cannot be used. It was introduced in
-  pytest 3.1, which means it is not available on xenial.  The more
-  limited mechanism it replaced was removed in pytest 4.0, so is not
-  available in focal or later.  The only available alternatives are to
-  write mark-requiring test instances as completely separate tests,
-  without utilising parameterisation, or to apply the mark to the
-  entire parameterized test (and therefore every test instance).
-
 Mocking and Assertions
 ----------------------
 
@@ -168,9 +146,9 @@ Test Argument Ordering
 .. [#fixture-list] This list of fixtures (with markup) can be
    reproduced by running::
 
-     py.test-3 --fixtures -q | grep "^[^ -]" | grep -v '\(no\|capturelog\)' | sort | sed 's/.*/* ``\0``/'
+     python3 -m pytest  --fixtures -q | grep "^[^ -]" | grep -v 'no tests ran in' | sort | sed 's/ \[session scope\]//g;s/.*/* ``\0``/g'
 
-   in a xenial lxd container with python3-pytest-catchlog installed.
+   in an ubuntu lxd container with python3-pytest installed.
 
 .. _pytest: https://docs.pytest.org/
 .. _pytest fixtures: https://docs.pytest.org/en/latest/fixture.html
diff --git a/tests/integration_tests/bugs/test_gh626.py b/tests/integration_tests/bugs/test_gh626.py
index 7c720143..b80b677a 100644
--- a/tests/integration_tests/bugs/test_gh626.py
+++ b/tests/integration_tests/bugs/test_gh626.py
@@ -8,7 +8,6 @@ import pytest
 import yaml
 
 from tests.integration_tests import random_mac_address
-from tests.integration_tests.clouds import ImageSpecification
 from tests.integration_tests.instances import IntegrationInstance
 
 MAC_ADDRESS = random_mac_address()
@@ -29,7 +28,6 @@ iface eth0 inet dhcp
     ethernet-wol g"""
 
 
-@pytest.mark.sru_2020_11
 @pytest.mark.lxd_container
 @pytest.mark.lxd_vm
 @pytest.mark.lxd_config_dict(
@@ -39,11 +37,6 @@ iface eth0 inet dhcp
     }
 )
 def test_wakeonlan(client: IntegrationInstance):
-    if ImageSpecification.from_os_image().release == "xenial":
-        eni = client.execute("cat /etc/network/interfaces.d/50-cloud-init.cfg")
-        assert eni.endswith(EXPECTED_ENI_END)
-        return
-
     netplan_cfg = client.execute("cat /etc/netplan/50-cloud-init.yaml")
     netplan_yaml = yaml.safe_load(netplan_cfg)
     assert "wakeonlan" in netplan_yaml["network"]["ethernets"]["eth0"]
diff --git a/tests/integration_tests/bugs/test_lp1898997.py b/tests/integration_tests/bugs/test_lp1898997.py
index 115bd34f..d8ea54c3 100644
--- a/tests/integration_tests/bugs/test_lp1898997.py
+++ b/tests/integration_tests/bugs/test_lp1898997.py
@@ -47,8 +47,6 @@ version: 2
 @pytest.mark.lxd_vm
 @pytest.mark.lxd_use_exec
 @pytest.mark.not_bionic
-@pytest.mark.not_xenial
-@pytest.mark.sru_2020_11
 @pytest.mark.ubuntu
 class TestInterfaceListingWithOpenvSwitch:
     def test_ovs_member_interfaces_not_excluded(self, client):
diff --git a/tests/integration_tests/conftest.py b/tests/integration_tests/conftest.py
index b14b6ad0..2e44ef29 100644
--- a/tests/integration_tests/conftest.py
+++ b/tests/integration_tests/conftest.py
@@ -45,17 +45,6 @@ os_list = ["ubuntu"]
 
 session_start_time = datetime.datetime.now().strftime("%y%m%d%H%M%S")
 
-XENIAL_LXD_VM_EXEC_MSG = """\
-The default xenial images do not support `exec` for LXD VMs.
-
-Specify an image known to work using:
-
-    OS_IMAGE=<image id>::ubuntu::xenial
-
-You can re-run specifically tests that require this by passing `-m
-lxd_use_exec` to pytest.
-"""
-
 
 def pytest_runtest_setup(item):
     """Skip tests on unsupported clouds.
@@ -101,7 +90,7 @@ def disable_subp_usage(request):
     pass
 
 
-@pytest.yield_fixture(scope="session")
+@pytest.fixture(scope="session")
 def session_cloud():
     if integration_settings.PLATFORM not in platforms.keys():
         raise ValueError(
@@ -246,16 +235,6 @@ def _client(request, fixture_utils, session_cloud: IntegrationCloud):
     if lxd_use_exec is not None:
         if not isinstance(session_cloud, _LxdIntegrationCloud):
             pytest.skip("lxd_use_exec requires LXD")
-        if isinstance(session_cloud, LxdVmCloud):
-            image_spec = ImageSpecification.from_os_image()
-            if image_spec.release == image_spec.image_id == "xenial":
-                # Why fail instead of skip?  We expect that skipped tests will
-                # be run in a different one of our usual battery of test runs
-                # (e.g. LXD-only tests are skipped on EC2 but will run in our
-                # normal LXD test runs).  This is not true of this test: it
-                # can't run in our usual xenial LXD VM test run, and it may not
-                # run anywhere else.  A failure flags up this discrepancy.
-                pytest.fail(XENIAL_LXD_VM_EXEC_MSG)
         launch_kwargs["execute_via_ssh"] = False
     local_launch_kwargs = {}
     if lxd_setup is not None:
@@ -276,21 +255,21 @@ def _client(request, fixture_utils, session_cloud: IntegrationCloud):
         _collect_logs(instance, request.node.nodeid, test_failed)
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def client(request, fixture_utils, session_cloud, setup_image):
     """Provide a client that runs for every test."""
     with _client(request, fixture_utils, session_cloud) as client:
         yield client
 
 
-@pytest.yield_fixture(scope="module")
+@pytest.fixture(scope="module")
 def module_client(request, fixture_utils, session_cloud, setup_image):
     """Provide a client that runs once per module."""
     with _client(request, fixture_utils, session_cloud) as client:
         yield client
 
 
-@pytest.yield_fixture(scope="class")
+@pytest.fixture(scope="class")
 def class_client(request, fixture_utils, session_cloud, setup_image):
     """Provide a client that runs once per class."""
     with _client(request, fixture_utils, session_cloud) as client:
diff --git a/tests/integration_tests/datasources/test_lxd_discovery.py b/tests/integration_tests/datasources/test_lxd_discovery.py
index da010813..eb2a4cf2 100644
--- a/tests/integration_tests/datasources/test_lxd_discovery.py
+++ b/tests/integration_tests/datasources/test_lxd_discovery.py
@@ -59,13 +59,9 @@ def test_lxd_datasource_discovery(client: IntegrationInstance):
     )
     if (
         client.settings.PLATFORM == "lxd_vm"
-        and ImageSpecification.from_os_image().release
-        in (
-            "xenial",
-            "bionic",
-        )
+        and ImageSpecification.from_os_image().release == "bionic"
     ):
-        # pycloudlib injects user.vendor_data for lxd_vm on bionic and xenial
+        # pycloudlib injects user.vendor_data for lxd_vm on bionic
         # to start the lxd-agent.
         # https://github.com/canonical/pycloudlib/blob/main/pycloudlib/\
         #    lxd/defaults.py#L13-L27
diff --git a/tests/integration_tests/modules/test_disk_setup.py b/tests/integration_tests/modules/test_disk_setup.py
index 22277331..8f9d5f40 100644
--- a/tests/integration_tests/modules/test_disk_setup.py
+++ b/tests/integration_tests/modules/test_disk_setup.py
@@ -20,7 +20,7 @@ def setup_and_mount_lxd_disk(instance: LXDInstance):
     )
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def create_disk():
     # 640k should be enough for anybody
     subp("dd if=/dev/zero of={} bs=1k count=640".format(DISK_PATH).split())
@@ -133,10 +133,9 @@ class TestPartProbeAvailability:
         assert sdb["children"][1]["name"] == "sdb2"
         assert sdb["children"][1]["mountpoint"] == "/mnt2"
 
-    # Not bionic or xenial because the LXD agent gets in the way of us
+    # Not bionic because the LXD agent gets in the way of us
     # changing the userdata
     @pytest.mark.not_bionic
-    @pytest.mark.not_xenial
     def test_disk_setup_when_mounted(
         self, create_disk, client: IntegrationInstance
     ):
diff --git a/tests/integration_tests/modules/test_lxd_bridge.py b/tests/integration_tests/modules/test_lxd_bridge.py
index 2cb3f4f3..3292a833 100644
--- a/tests/integration_tests/modules/test_lxd_bridge.py
+++ b/tests/integration_tests/modules/test_lxd_bridge.py
@@ -33,8 +33,6 @@ class TestLxdBridge:
         """Check that the expected LXD binaries are installed"""
         assert class_client.execute(["which", binary_name]).ok
 
-    @pytest.mark.not_xenial
-    @pytest.mark.sru_2020_11
     def test_bridge(self, class_client):
         """Check that the given bridge is configured"""
         cloud_init_log = class_client.read_from_file("/var/log/cloud-init.log")
diff --git a/tests/integration_tests/modules/test_users_groups.py b/tests/integration_tests/modules/test_users_groups.py
index 3d1358ce..fddff681 100644
--- a/tests/integration_tests/modules/test_users_groups.py
+++ b/tests/integration_tests/modules/test_users_groups.py
@@ -106,7 +106,6 @@ def test_sudoers_includedir(client: IntegrationInstance):
     https://github.com/canonical/cloud-init/pull/783
     """
     if ImageSpecification.from_os_image().release in [
-        "xenial",
         "bionic",
         "focal",
     ]:
diff --git a/tests/unittests/cmd/devel/test_hotplug_hook.py b/tests/unittests/cmd/devel/test_hotplug_hook.py
index 842e8dfd..5ecb5969 100644
--- a/tests/unittests/cmd/devel/test_hotplug_hook.py
+++ b/tests/unittests/cmd/devel/test_hotplug_hook.py
@@ -16,7 +16,7 @@ hotplug_args = namedtuple("hotplug_args", "udevaction, subsystem, devpath")
 FAKE_MAC = "11:22:33:44:55:66"
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def mocks():
     m_init = mock.MagicMock(spec=Init)
     m_distro = mock.MagicMock(spec=Distro)
diff --git a/tests/unittests/config/test_cc_install_hotplug.py b/tests/unittests/config/test_cc_install_hotplug.py
index 3bd44aba..e67fce60 100644
--- a/tests/unittests/config/test_cc_install_hotplug.py
+++ b/tests/unittests/config/test_cc_install_hotplug.py
@@ -12,7 +12,7 @@ from cloudinit.config.cc_install_hotplug import (
 from cloudinit.event import EventScope, EventType
 
 
-@pytest.yield_fixture()
+@pytest.fixture()
 def mocks():
     m_update_enabled = mock.patch("cloudinit.stages.update_event_enabled")
     m_write = mock.patch("cloudinit.util.write_file", autospec=True)
diff --git a/tests/unittests/distros/test_networking.py b/tests/unittests/distros/test_networking.py
index 635f6901..274647cb 100644
--- a/tests/unittests/distros/test_networking.py
+++ b/tests/unittests/distros/test_networking.py
@@ -13,7 +13,7 @@ from cloudinit.distros.networking import (
 )
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def generic_networking_cls():
     """Returns a direct Networking subclass which errors on /sys usage.
 
@@ -40,7 +40,7 @@ def generic_networking_cls():
         yield TestNetworking
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def sys_class_net(tmpdir):
     sys_class_net_path = tmpdir.join("sys/class/net")
     sys_class_net_path.ensure_dir()
diff --git a/tests/unittests/sources/test_lxd.py b/tests/unittests/sources/test_lxd.py
index ad1508a0..e11c3746 100644
--- a/tests/unittests/sources/test_lxd.py
+++ b/tests/unittests/sources/test_lxd.py
@@ -57,7 +57,7 @@ def lxd_metadata():
     return LXD_V1_METADATA
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def lxd_ds(request, paths, lxd_metadata):
     """
     Return an instantiated DataSourceLXD.
diff --git a/tests/unittests/sources/test_oracle.py b/tests/unittests/sources/test_oracle.py
index e0e79c8c..356b3738 100644
--- a/tests/unittests/sources/test_oracle.py
+++ b/tests/unittests/sources/test_oracle.py
@@ -93,7 +93,7 @@ def metadata_version():
     return 2
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def oracle_ds(request, fixture_utils, paths, metadata_version):
     """
     Return an instantiated DataSourceOracle.
@@ -649,7 +649,7 @@ class TestCommon_GetDataBehaviour:
     separate class for that case.)
     """
 
-    @pytest.yield_fixture(params=[True, False])
+    @pytest.fixture(params=[True, False])
     def parameterized_oracle_ds(self, request, oracle_ds):
         """oracle_ds parameterized for iSCSI and non-iSCSI root respectively"""
         is_iscsi_root = request.param
diff --git a/tests/unittests/sources/test_vmware.py b/tests/unittests/sources/test_vmware.py
index dcdbda89..dd331349 100644
--- a/tests/unittests/sources/test_vmware.py
+++ b/tests/unittests/sources/test_vmware.py
@@ -57,7 +57,7 @@ runcmd:
 """
 
 
-@pytest.yield_fixture(autouse=True)
+@pytest.fixture(autouse=True)
 def common_patches():
     with mock.patch("cloudinit.util.platform.platform", return_value="Linux"):
         with mock.patch.multiple(
diff --git a/tests/unittests/test_features.py b/tests/unittests/test_features.py
index 141de55b..794a9654 100644
--- a/tests/unittests/test_features.py
+++ b/tests/unittests/test_features.py
@@ -12,7 +12,7 @@ import pytest
 import cloudinit
 
 
-@pytest.yield_fixture()
+@pytest.fixture()
 def create_override(request):
     """
     Create a feature overrides file and do some module wizardry to make
diff --git a/tests/unittests/test_net_activators.py b/tests/unittests/test_net_activators.py
index 0e3ab43f..3c29e2f7 100644
--- a/tests/unittests/test_net_activators.py
+++ b/tests/unittests/test_net_activators.py
@@ -39,7 +39,7 @@ NETPLAN_CALL_LIST = [
 ]
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def available_mocks():
     mocks = namedtuple("Mocks", "m_which, m_file")
     with patch("cloudinit.subp.which", return_value=True) as m_which:
@@ -47,7 +47,7 @@ def available_mocks():
             yield mocks(m_which, m_file)
 
 
-@pytest.yield_fixture
+@pytest.fixture
 def unavailable_mocks():
     mocks = namedtuple("Mocks", "m_which, m_file")
     with patch("cloudinit.subp.which", return_value=False) as m_which:
diff --git a/tests/unittests/test_stages.py b/tests/unittests/test_stages.py
index be1a0787..3214410b 100644
--- a/tests/unittests/test_stages.py
+++ b/tests/unittests/test_stages.py
@@ -512,7 +512,7 @@ class TestInit_InitializeFilesystem:
     TODO: Expand these tests to cover all of _initialize_filesystem's behavior.
     """
 
-    @pytest.yield_fixture
+    @pytest.fixture
     def init(self, paths):
         """A fixture which yields a stages.Init instance with paths and cfg set
 
diff --git a/tests/unittests/test_util.py b/tests/unittests/test_util.py
index e2bfe9d2..3765511b 100644
--- a/tests/unittests/test_util.py
+++ b/tests/unittests/test_util.py
@@ -1127,7 +1127,7 @@ class TestMountCb:
     TODO: Test the if/else branch that actually performs the mounting operation
     """
 
-    @pytest.yield_fixture
+    @pytest.fixture
     def already_mounted_device_and_mountdict(self):
         """Mock an already-mounted device, and yield (device, mount dict)"""
         device = "/dev/fake0"
diff --git a/tox.ini b/tox.ini
index 034ee9a4..57d18cdb 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,58 +1,52 @@
 [tox]
-envlist = py3, xenial-dev, flake8, pylint, black, isort
+envlist = py3, lowest-supported-dev, flake8, pylint, black, isort
 recreate = True
 
 [testenv]
-commands = {envpython} -m pytest {posargs:tests/unittests}
+basepython = python3
 setenv =
     LC_ALL = en_US.utf-8
 passenv=
     PYTEST_ADDOPTS
 
-[testenv:flake8]
-basepython = python3
+[flake_env]
+envdir = {toxworkdir}/.flake_env
 deps =
     flake8==3.9.2
-commands = {envpython} -m flake8 {posargs:cloudinit/ tests/ tools/ setup.py}
-
-# https://github.com/gabrielfalcao/HTTPretty/issues/223
-setenv =
-    LC_ALL = en_US.utf-8
-
-[testenv:pylint]
-basepython = python3
-deps =
-    # requirements
     pylint==2.11.1
-    # test-requirements because unit tests are now present in cloudinit tree
+    black==21.12b0
+    isort==5.10.1
     -r{toxinidir}/test-requirements.txt
     -r{toxinidir}/integration-requirements.txt
+
+[testenv:flake8]
+envdir = {[flake_env]envdir}
+deps = {[flake_env]deps}
+commands = {envpython} -m flake8 {posargs:cloudinit/ tests/ tools/ setup.py}
+
+[testenv:pylint]
+envdir = {[flake_env]envdir}
+deps = {[flake_env]deps}
 commands = {envpython} -m pylint {posargs:cloudinit tests tools}
 
 [testenv:black]
-basepython = python3
-deps =
-    # requirements
-    black==21.12b0
+envdir = {[flake_env]envdir}
+deps = {[flake_env]deps}
 commands = {envpython} -m black . --check
 
 [testenv:isort]
-basepython = python3
-deps =
-    isort==5.10.1
+envdir = {[flake_env]envdir}
+deps = {[flake_env]deps}
 commands = {envpython} -m isort . --check-only
 
 [testenv:format]
-basepython = python3
-deps =
-    black==21.12b0
-    isort==5.10.1
+envdir = {[flake_env]envdir}
+deps = {[flake_env]deps}
 commands =
     {envpython} -m isort .
     {envpython} -m black .
 
 [testenv:py3]
-basepython = python3
 deps =
     -r{toxinidir}/test-requirements.txt
 commands = {envpython} -m pytest \
@@ -60,84 +54,56 @@ commands = {envpython} -m pytest \
             {posargs:--cov=cloudinit --cov-branch \
             tests/unittests}
 
-[testenv:py27]
-basepython = python2.7
-deps = -r{toxinidir}/test-requirements.txt
+[lowest-supported-deps]
+# Tox is going to install requirements from pip. This is fine for
+# testing python version compatibility, but when we build cloud-init, we are
+# building against the dependencies in the OS repo, not pip. The OS
+# dependencies will generally be older than what is found in pip.
 
-[flake8]
-# E203: whitespace before ':', doesn't adhere to pep8 or black formatting
-# W503: line break before binary operator
-ignore=E203,W503
-exclude = .venv,.tox,dist,doc,*egg,.git,build,tools
-per-file-ignores =
-    cloudinit/cmd/main.py:E402
+# To obtain these versions, check the versions of these libraries
+# in the oldest support Ubuntu distro.
 
-[testenv:doc]
-basepython = python3
-deps =
-    -r{toxinidir}/doc-requirements.txt
-commands =
-    {envpython} -m sphinx {posargs:doc/rtd doc/rtd_html}
-    doc8 doc/rtd
-
-[xenial-shared-deps]
-# The version of pytest in xenial doesn't work with Python 3.8, so we define
-# two xenial environments: [testenv:xenial] runs the tests with exactly the
-# version of pytest present in xenial, and is used in CI.  [testenv:xenial-dev]
-# runs the tests with the lowest version of pytest that works with Python 3.8,
-# 3.0.7, but keeps the other dependencies at xenial's level.
-#
-# (This section is not a testenv, it is used to maintain a single definition of
-# the dependencies shared between the two xenial testenvs.)
+# httpretty isn't included here because python2.7 requires a higher version
+# than whats run on bionic, so we need two different definitions.
 deps =
-    # requirements
-    jinja2==2.8
-    pyyaml==3.11
-    oauthlib==1.0.3
-    pyserial==3.0.1
+    jinja2==2.10
+    oauthlib==2.0.6
+    pyserial==3.4
     configobj==5.0.6
-    requests==2.9.1
-    jsonschema
+    pyyaml==3.12
+    requests==2.18.4
+    jsonpatch==1.16
+    jsonschema==2.6.0
+    netifaces==0.10.4
     # test-requirements
-    pytest-catchlog==1.2.1
-
-[testenv:xenial]
-# When updating this commands definition, also update the definition in
-# [testenv:xenial-dev].  See the comment there for details.
-commands =
-  python ./tools/pipremove jsonschema
-  python -m pytest {posargs:tests/unittests}
-basepython = python3
+    pytest==3.3.2
+    pytest-cov==2.5.1
+    # Needed by pytest and default causes failures
+    attrs==17.4.0
+
+[testenv:lowest-supported]
+# This definition will run on bionic with the version of httpretty
+# that runs there
 deps =
-    # Refer to the comment in [xenial-shared-deps] for details
-    {[xenial-shared-deps]deps}
-    httpretty==0.8.6
-    jsonpatch==1.10
-    pytest==2.8.7
-
-[testenv:xenial-dev]
-# This should be:
-#   commands = {[testenv:xenial]commands}
-# but the version of pytest in xenial has a bug
-# (https://github.com/tox-dev/tox/issues/208) which means that the {posargs}
-# substitution variable is misparsed and causes a traceback.  Ensure that any
-# changes here are reflected in [testenv:xenial].
-commands =
-  python ./tools/pipremove jsonschema
-  python -m pytest {posargs:tests/unittests}
-basepython = {[testenv:xenial]basepython}
+    {[lowest-supported-deps]deps}
+    httpretty==0.8.14
+commands = {[testenv:py3]commands}
+
+[testenv:lowest-supported-dev]
+# The oldest httpretty version to work with Python 3.7+ is 0.9.5,
+# because it is the first to include this commit:
+# https://github.com/gabrielfalcao/HTTPretty/commit/5776d97da3992b9071db5e21faf175f6e8729060
 deps =
-    # Refer to the comment in [xenial-shared-deps] for details
-    {[xenial-shared-deps]deps}
-    # httpretty in xenial is 0.8.6, not 0.9.5.  The oldest version to work with
-    # Python 3.7+ is 0.9.5, because it is the first to include this commit:
-    # https://github.com/gabrielfalcao/HTTPretty/commit/5776d97da3992b9071db5e21faf175f6e8729060
+    {[lowest-supported-deps]deps}
     httpretty==0.9.5
-    # jsonpatch in xenial is 1.10, not 1.19 (#839779). The oldest version
-    # to work with python3.6 is 1.16 as found in Artful.  To keep default
-    # invocation of 'tox' happy, accept the difference in version here.
-    jsonpatch==1.16
-    pytest==3.0.7
+commands = {[testenv:py3]commands}
+
+[testenv:doc]
+deps =
+    -r{toxinidir}/doc-requirements.txt
+commands =
+    {envpython} -m sphinx {posargs:doc/rtd doc/rtd_html}
+    doc8 doc/rtd
 
 [testenv:tip-flake8]
 commands = {envpython} -m flake8 {posargs:cloudinit/ tests/ tools/ setup.py}
@@ -152,37 +118,36 @@ deps =
     -r{toxinidir}/test-requirements.txt
     -r{toxinidir}/integration-requirements.txt
 
-# Until Xenial tox support is dropped or bumps to tox:2.3.2, reflect changes to
-# deps into testenv:integration-tests-ci: commands, passenv and deps.
-# This is due to (https://github.com/tox-dev/tox/issues/208) which means that
-# the {posargs} handling and substitutions won't do what we want until tox 2.3.2
-# Once Xenial is dropped, integration-tests-ci can use proper substitution
-# commands = {[testenv:integration-tests]commands}
 [testenv:integration-tests]
-basepython = python3
 commands = {envpython} -m pytest --log-cli-level=INFO {posargs:tests/integration_tests}
-passenv = CLOUD_INIT_* SSH_AUTH_SOCK OS_*
 deps =
     -r{toxinidir}/integration-requirements.txt
+passenv = CLOUD_INIT_* SSH_AUTH_SOCK OS_*
 
 [testenv:integration-tests-ci]
-commands = {envpython} -m pytest --log-cli-level=INFO {posargs:tests/integration_tests}
+commands = {[testenv:integration-tests]commands}
+deps = {[testenv:integration-tests]deps}
 passenv = CLOUD_INIT_* SSH_AUTH_SOCK OS_* TRAVIS
-deps =
-    -r{toxinidir}/integration-requirements.txt
 setenv =
     PYTEST_ADDOPTS="-m ci and not adhoc"
 
 [testenv:integration-tests-jenkins]
-commands = {envpython} -m pytest --log-cli-level=INFO {posargs:tests/integration_tests}
+commands = {[testenv:integration-tests]commands}
+deps = {[testenv:integration-tests]deps}
 passenv = *_proxy CLOUD_INIT_* SSH_AUTH_SOCK OS_* GOOGLE_* GCP_*
-deps =
-    -r{toxinidir}/integration-requirements.txt
 setenv =
     PYTEST_ADDOPTS="-m not adhoc"
 
+[flake8]
+# E203: whitespace before ':', doesn't adhere to pep8 or black formatting
+# W503: line break before binary operator
+ignore=E203,W503
+exclude = .venv,.tox,dist,doc,*egg,.git,build,tools
+per-file-ignores =
+    cloudinit/cmd/main.py:E402
+
 [pytest]
-# TODO: s/--strict/--strict-markers/ once xenial support is dropped
+# TODO: s/--strict/--strict-markers/ once pytest version is high enough
 testpaths = tests/unittests
 addopts = --strict
 log_format = %(asctime)s %(levelname)-9s %(name)s:%(filename)s:%(lineno)d %(message)s
@@ -202,7 +167,6 @@ markers =
     lxd_setup: specify callable to be called between init and start
     lxd_use_exec: `execute` will use `lxc exec` instead of SSH
     lxd_vm: test will only run in LXD VM
-    not_xenial: test cannot run on the xenial release
     not_bionic: test cannot run on the bionic release
     no_container: test cannot run in a container
     user_data: the user data to be passed to the test instance