omit updates of unchanged values within short time

Sometimes it happens, that the same value determined once is
assigned several times to a parameter within a very short period.
Sending multiple updates is not useful in this case.

Change-Id: Icea66934c831fd9b2eac7d0394a124d002469914
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27091
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

test/test_modules.py

@@ -34,7 +34,11 @@ from secop.poller import BasicPoller
 
 
 class DispatcherStub:
-    OMIT_UNCHANGED_WITHIN = 0
+    # the first update from the poller comes a very short time after the
+    # initial value from the timestamp. However, in the test below
+    # the second update happens after the updates dict is cleared
+    # -> we have to inhibit the 'omit unchanged update' feature
+    omit_unchanged_within = 0
 
     def __init__(self, updates):
         self.updates = updates