tests/py: Enable umockdev based tests

We re-exec the test case in pytest_configure if the LD_PRELOAD doesn't
contain libumockdev-preload.so. Even if the system doesn't have it, it
will show up in the environment and we can continue.

It also sets the UMOCKDEV_DIR env for the portal frontend. In theory
dbusmock should already do this for us but it doesn't seem to be
working.

tests/__init__.py

@@ -336,7 +336,8 @@ def __init__(
         self,
         dbus_test_case,
         portal_name: str,
-        app_id: str = "org.example.App"
+        app_id: str = "org.example.App",
+        umockdev = None,
     ):
         self.dbus_test_case = dbus_test_case
         self.portal_name = portal_name
@@ -346,6 +347,7 @@ def __init__(
         self.portal_interfaces: Dict[str, dbus.Interface] = {}
         self.app_id = app_id
         self.busses = {dbusmock.BusType.SYSTEM: {}, dbusmock.BusType.SESSION: {}}
+        self.umockdev = umockdev
 
     @property
     def interface_name(self) -> str:
@@ -443,6 +445,9 @@ def start_xdp(self):
         env["XDG_CURRENT_DESKTOP"] = "test"
         env["XDG_DESKTOP_PORTAL_TEST_APP_ID"] = self.app_id
 
+        if self.umockdev:
+            env["UMOCKDEV_DIR"] = self.umockdev.get_root_dir()
+
         self.start_dbus_monitor()
         self.start_portal_frontend(env)
         self.start_permission_store(env)

tests/conftest.py

@@ -7,15 +7,25 @@
 import pytest
 import dbusmock
 import os
+import sys
 import tempfile
 
 from tests import PortalMock
 
 
 def pytest_configure():
+    ensure_umockdev_loaded()
     create_test_dirs()
 
 
+def ensure_umockdev_loaded():
+    umockdev_preload = "libumockdev-preload.so"
+    preload = os.environ.get("LD_PRELOAD", "")
+    if umockdev_preload not in preload:
+        os.environ["LD_PRELOAD"] = f"{umockdev_preload}:{preload}"
+        os.execv(sys.executable, [sys.executable] + sys.argv)
+
+
 def create_test_dirs():
     test_root = tempfile.TemporaryDirectory(
         prefix='xdp-testroot-',
@@ -124,13 +134,22 @@ def app_id():
     return "org.example.App"
 
 
+@pytest.fixture
+def umockdev():
+    """
+    Default fixture providing a umockdev testbed
+    """
+    return None
+
+
 @pytest.fixture
 def portal_mock(
     dbus_test_case,
     portal_name,
     required_templates,
     template_params,
     app_id,
+    umockdev,
 ) -> PortalMock:
     """
     Fixture yielding a PortalMock object with the impl started, if applicable.
@@ -139,6 +158,7 @@ def portal_mock(
         dbus_test_case,
         portal_name,
         app_id=app_id,
+        umockdev=umockdev,
     )
 
     for template, params in required_templates.items():