tests/py: Move portal DUT environment to caller

This way it becomes reusable when we want to start more components.

tests/__init__.py

@@ -425,10 +425,27 @@ def start_xdp(self):
         Start the xdg-desktop-portal process
         """
 
+        portal_dir = (
+            Path(os.getenv("G_TEST_BUILDDIR") or "tests")
+            / "portals"
+            / "test"
+        )
+
+        if not portal_dir.exists():
+            raise FileNotFoundError(
+                f"{portal_dir} does not exist, try running from meson build dir or setting G_TEST_SRCDIR"
+            )
+
+        env = os.environ.copy()
+        env["G_DEBUG"] = "fatal-criticals"
+        env["XDG_DESKTOP_PORTAL_DIR"] = portal_dir
+        env["XDG_CURRENT_DESKTOP"] = "test"
+        env["XDG_DESKTOP_PORTAL_TEST_APP_ID"] = self.app_id
+
         self.start_dbus_monitor()
-        self.start_portal_frontend()
+        self.start_portal_frontend(env)
 
-    def start_portal_frontend(self):
+    def start_portal_frontend(self, env):
         # This roughly resembles test-portals.c and glib's test behavior
         # but preferences in-tree testing by running pytest in meson's
         # project_build_root
@@ -448,20 +465,7 @@ def start_portal_frontend(self):
                 f"{portal_frontend} does not exist, try running from meson build dir or setting G_TEST_BUILDDIR"
             )
 
-        portal_dir = Path(os.getenv("G_TEST_BUILDDIR") or "tests") / "portals" / "test"
-        if not portal_dir.exists():
-            raise FileNotFoundError(
-                f"{portal_dir} does not exist, try running from meson build dir or setting G_TEST_SRCDIR"
-            )
-
-        argv = [portal_frontend]
-        env = os.environ.copy()
-        env["G_DEBUG"] = "fatal-criticals"
-        env["XDG_DESKTOP_PORTAL_DIR"] = portal_dir
-        env["XDG_CURRENT_DESKTOP"] = "test"
-        env["XDG_DESKTOP_PORTAL_TEST_APP_ID"] = self.app_id
-
-        portal_frontend = subprocess.Popen(argv, env=env)
+        portal_frontend = subprocess.Popen([portal_frontend], env=env)
 
         for _ in range(50):
             if self.dbus_test_case.dbus_con.name_has_owner("org.freedesktop.portal.Desktop"):
@@ -478,8 +482,7 @@ def start_dbus_monitor(self):
         if not os.getenv("XDP_DBUS_MONITOR"):
             return
 
-        argv = ["dbus-monitor", "--session"]
-        self.dbus_monitor = subprocess.Popen(argv)
+        self.dbus_monitor = subprocess.Popen(["dbus-monitor", "--session"])
 
     def tearDown(self):
         if self.dbus_monitor: