tests: Wait for memory monitor to be able to handle signals before testing

This fixes a race condition which frequently caused the
`memory-monitor-dbus.py` test to fail.

The registration of the `LowMemoryMonitor` object on the bus, and the
`GMemoryMonitorDBus`’s connection to the warning signal raced, such that
it was possible for the mock `LowMemoryMonitor` to emit a warning signal
before the `GMemoryMonitorDBus` proxy was listening, and hence the proxy
would never see the signal.

Fix this by explicitly synchronising the two before proceeding to the
tests.

Make the same changes in the `memory-monitor-portal.py` test too, even
though that one was not failing. This should remove the need for a 2s
wait on every test run.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Fixes: #2887

gio/tests/memory-monitor-dbus.py.in

@@ -16,7 +16,6 @@ import sys
 import subprocess
 import fcntl
 import os
-import time
 
 import taptestrunner
 
@@ -71,6 +70,19 @@ try:
             self.mainloop = GLib.MainLoop()
             self.main_context = self.mainloop.get_context()
 
+            # The LowMemoryMonitor API is stateless: it doesn’t expose any
+            # properties, just a warning signal. Emit the signal in a loop until
+            # the GMemoryMonitor instance has initialised and synchronised to
+            # the right state.
+            def emit_warning(level):
+                self.dbusmock.EmitWarning(level)
+                return GLib.SOURCE_CONTINUE
+
+            idle_id = GLib.idle_add(emit_warning, 0)
+            while self.last_warning != 0:
+                self.main_context.iteration(True)
+            GLib.source_remove(idle_id)
+
         def tearDown(self):
             self.p_mock.terminate()
             self.p_mock.wait()
@@ -105,13 +117,6 @@ try:
         def test_low_memory_warning_signal(self):
             '''LowMemoryWarning signal'''
 
-            # Wait 2 seconds
-            timeout = 2
-            while timeout > 0:
-                time.sleep(0.5)
-                timeout -= 0.5
-                self.main_context.iteration(False)
-
             self.dbusmock.EmitWarning(100)
             # Wait 2 seconds or until warning
             self.assertEventually(lambda: self.last_warning == 100, "'100' low-memory warning not received", 2)

gio/tests/memory-monitor-portal.py.in

@@ -16,7 +16,6 @@ import sys
 import subprocess
 import fcntl
 import os
-import time
 
 import taptestrunner
 
@@ -80,6 +79,19 @@ try:
             self.mainloop = GLib.MainLoop()
             self.main_context = self.mainloop.get_context()
 
+            # The LowMemoryMonitor API is stateless: it doesn’t expose any
+            # properties, just a warning signal. Emit the signal in a loop until
+            # the GMemoryMonitor instance has initialised and synchronised to
+            # the right state.
+            def emit_warning(level):
+                self.dbusmock.EmitWarning(level)
+                return GLib.SOURCE_CONTINUE
+
+            idle_id = GLib.idle_add(self.emit_warning, 0)
+            while self.last_warning != 0:
+                self.main_context.iteration(True)
+            GLib.source_remove(idle_id)
+
         def tearDown(self):
             self.p_mock.terminate()
             self.p_mock.wait()
@@ -113,13 +125,6 @@ try:
         def test_low_memory_warning_portal_signal(self):
             '''LowMemoryWarning signal'''
 
-            # Wait 2 seconds
-            timeout = 2
-            while timeout > 0:
-                time.sleep(0.5)
-                timeout -= 0.5
-                self.main_context.iteration(False)
-
             self.dbusmock.EmitWarning(100)
             # Wait 2 seconds or until warning
             self.assertEventually(lambda: self.last_warning == 100, "'100' low-memory warning not received", 2)