build gio/tests/gdbus-connection with this patch:

diff --git a/gio/tests/gdbus-sessionbus.c b/gio/tests/gdbus-sessionbus.c
index f39583c..509d00d 100644
--- a/gio/tests/gdbus-sessionbus.c
+++ b/gio/tests/gdbus-sessionbus.c
@@ -299,2 +299,4 @@ session_bus_down_with_address (const gchar *address)
   g_hash_table_remove (session_bus_address_to_pid, address);
+
+  g_usleep (100000);
 }

and it will reliably hang at the end of test_connection_life_cycle(). It appears that if the connection gets closed before session_bus_down() returns, then c will have a ref count of 2 when it returns instead of 1.