integration: completely remove LocalHarness. (#912)

The LocalHarness is a harness used for running integration tests
on the local machine where the tests are directly invoked
(be it via `tox`, `pytest`, etc).

It presents numerous limitations (can't run any multi-node tests)
and poses a lot of potential risks (cleanup failing in case of
fatal errors in the test fixtures) which outweighs most of its
convenience benefits (especially when compared to the LXD
substrate).

This patch completely removes the LocalHarness and all references to it
from the documentation, making LXD the new default.

Signed-off-by: Nashwan Azhari <[email protected]>

tests/integration/README.md

@@ -2,7 +2,7 @@
 
 ## Overview
 
-End to end tests are written in Python. They are built on top of a [Harness](./tests/conftest.py) fixture so that they can run on multiple environments like LXD, Multipass, Juju, or the local machine.
+End to end tests are written in Python. They are built on top of a [Harness](./tests/conftest.py) fixture so that they can run on multiple environments like LXD, Multipass, or Juju.
 
 End to end tests can be configured using environment variables. You can see all available options in [./tests/config.py](./tests/config.py).
 
@@ -28,17 +28,6 @@ In general, all end to end tests will require specifying the local path to the s
 
 End to end tests are typically run with: `cd tests/integration && tox -e integration`
 
-### Running end to end tests on the local machine
-
-```bash
-export TEST_SNAP=$PWD/k8s.snap
-export TEST_SUBSTRATE=local
-
-cd tests/integration && tox -e integration
-```
-
-> *NOTE*: When running locally, end to end tests that create more than one instance will fail.
-
 ### Running end to end tests on LXD containers
 
 First, make sure that you have initialized LXD:

tests/integration/tests/conftest.py

@@ -81,17 +81,15 @@ def _generate_inspection_report(h: harness.Harness, instance_id: str):
 @pytest.fixture(scope="session")
 def h() -> harness.Harness:
     LOG.debug("Create harness for %s", config.SUBSTRATE)
-    if config.SUBSTRATE == "local":
-        h = harness.LocalHarness()
-    elif config.SUBSTRATE == "lxd":
+    if config.SUBSTRATE == "lxd":
         h = harness.LXDHarness()
     elif config.SUBSTRATE == "multipass":
         h = harness.MultipassHarness()
     elif config.SUBSTRATE == "juju":
         h = harness.JujuHarness()
     else:
         raise harness.HarnessError(
-            "TEST_SUBSTRATE must be one of: local, lxd, multipass, juju"
+            "TEST_SUBSTRATE must be one of: lxd, multipass, juju"
         )
 
     yield h

tests/integration/tests/test_util/config.py

@@ -44,8 +44,8 @@
 SNAP_NAME = os.getenv("TEST_SNAP_NAME") or "k8s"
 
 # SUBSTRATE is the substrate to use for running the integration tests.
-# One of 'local' (default), 'lxd', 'juju', or 'multipass'.
-SUBSTRATE = os.getenv("TEST_SUBSTRATE") or "local"
+# One of 'lxd' (default), 'juju', or 'multipass'.
+SUBSTRATE = os.getenv("TEST_SUBSTRATE") or "lxd"
 
 # SKIP_CLEANUP can be used to prevent machines to be automatically destroyed
 # after the tests complete.

tests/integration/tests/test_util/harness/__init__.py

@@ -3,7 +3,6 @@
 #
 from test_util.harness.base import Harness, HarnessError, Instance
 from test_util.harness.juju import JujuHarness
-from test_util.harness.local import LocalHarness
 from test_util.harness.lxd import LXDHarness
 from test_util.harness.multipass import MultipassHarness
 
@@ -12,7 +11,6 @@
     Harness,
     Instance,
     JujuHarness,
-    LocalHarness,
     LXDHarness,
     MultipassHarness,
 ]

tests/integration/tests/test_util/harness/base.py

@@ -43,8 +43,7 @@ def __str__(self) -> str:
 
 class Harness:
     """Abstract how integration tests can start and manage multiple machines. This allows
-    writing integration tests that can run on the local machine, LXD, or Multipass with minimum
-    effort.
+    writing integration tests that can run on LXD, or Multipass with minimum effort.
     """
 
     name: str