[gnome-settings-daemon] power: Add helper to read plugin log during test

[Benjamin Berg <bberg src gnome org>]

commit 450a9361915ad08ee5716f65d7858683e2c160e5
Author: Benjamin Berg <bberg redhat com>
Date:   Thu Jan 4 15:46:01 2018 +0100

    power: Add helper to read plugin log during test
    
    Add a generic helper to find needles in the gsd-power plugin log.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=792210

 plugins/power/test.py |   25 +++++++++++++++++++++++++
 1 files changed, 25 insertions(+), 0 deletions(-)
---
diff --git a/plugins/power/test.py b/plugins/power/test.py
index 938064f..b88adc6 100755
--- a/plugins/power/test.py
+++ b/plugins/power/test.py
@@ -291,6 +291,31 @@ class PowerPluginTest(gsdtestcase.GSDTestCase):
             self.assertTrue(b' Suspend' in log, 'missing Suspend request')
             self.assertFalse(b' Hibernate' in log, 'unexpected Hibernate request')
 
+    def check_plugin_log(self, needle, timeout=0, failmsg=None):
+        '''Check that needle is found in the log within the given timeout.
+        Returns immediately when found.
+
+        Fail after the given timeout.
+        '''
+        # Fast path if the message was already logged
+        log = self.plugin_log.read()
+        if needle in log:
+            return
+
+        while timeout > 0:
+            time.sleep(0.5)
+            timeout -= 0.5
+
+            # read new data (lines) from the log
+            log = self.plugin_log.read()
+            if needle in log:
+                break
+        else:
+            if failmsg is not None:
+                self.fail(failmsg)
+            else:
+                self.fail('timed out waiting for needle "%s"' % needle)
+
     def check_no_dim(self, seconds):
         '''Check that mode is not set to dim in the given time'''