Minimize D-Bus requirements for tests (#5265)

This PR minimizes the D-Bus requirements for tests. It does this by
using dbus-daemon directly instead of dbus-launch. The latter is meant
for graphical applications and therefor has X11 dependencies. It also
leaves the D-Bus daemon running after the tests are done. This will
accumulate dbus-daemon processes over time which is not ideal.

I've also considered using dbus-run-session since it is meant to launch
processes with a private D-Bus session. For Python tests one could
launch it like so:
dbus-run-session -- python3 -m pytest ...

Then `DBUS_SESSION_BUS_ADDRESS` would be used automatically by the
`MessageBus` class. However, to keep the current behavior of the tests,
launching the D-Bus daemon manually is the better option.

.github/workflows/ci.yaml

@@ -313,7 +313,7 @@ jobs:
       - name: Install additional system dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y --no-install-recommends libpulse0 libudev1 dbus dbus-x11
+          sudo apt-get install -y --no-install-recommends libpulse0 libudev1 dbus-daemon
       - name: Register Python problem matcher
         run: |
           echo "::add-matcher::.github/workflows/matchers/python.json"

tests/conftest.py

@@ -1,6 +1,7 @@
 """Common test functions."""
 
 import asyncio
+from collections.abc import AsyncGenerator, Generator
 from functools import partial
 from inspect import unwrap
 import os
@@ -115,20 +116,28 @@ async def docker() -> DockerAPI:
 
 
 @pytest.fixture(scope="session")
-def dbus_session() -> None:
-    """Start a dbus session."""
-    dbus_launch = subprocess.run(["dbus-launch"], stdout=subprocess.PIPE, check=False)
-    envs = dbus_launch.stdout.decode(encoding="utf-8").rstrip()
+def dbus_session() -> Generator[str, None, None]:
+    """Start a dbus session.
 
-    for env in envs.split("\n"):
-        name, value = env.split("=", 1)
-        os.environ[name] = value
+    Returns session address.
+    """
+    with subprocess.Popen(
+        [
+            "dbus-daemon",
+            "--nofork",
+            "--print-address",
+            "--session",
+        ],
+        stdout=subprocess.PIPE,
+    ) as proc:
+        yield proc.stdout.readline().decode("utf-8").strip()
+        proc.terminate()
 
 
 @pytest.fixture
-async def dbus_session_bus(dbus_session) -> MessageBus:
+async def dbus_session_bus(dbus_session) -> AsyncGenerator[MessageBus, None, None]:
     """Return message bus connected to session dbus."""
-    bus = await MessageBus(bus_type=BusType.SESSION).connect()
+    bus = await MessageBus(bus_type=BusType.SESSION, bus_address=dbus_session).connect()
     yield bus
     bus.disconnect()