an error on a write must not send an error update

Change-Id: I07a991bcf26e87121160a2e604f8842eba23ebaf
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/35281
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

frappy/modulebase.py

@@ -188,10 +188,8 @@ class HasAccessibles(HasProperties):
                                 if new_value is Done:  # TODO: to be removed when all code using Done is updated
                                     return getattr(self, pname)
                                 new_value = value if new_value is None else validate(new_value)
-                        except Exception as e:
-                            if isinstance(e, SECoPError):
+                        except SECoPError as e:
                             e.raising_methods.append(f'{self.name}.write_{pname}')
-                            self.announceUpdate(pname, err=e)
                             raise
                         self.announceUpdate(pname, new_value, validate=False)
                         return new_value
@@ -516,13 +514,13 @@ class Module(HasAccessibles):
         with self.updateLock:
             pobj = self.parameters[pname]
             timestamp = timestamp or time.time()
+            changed = False
             if not err:
                 try:
                     if validate:
                         value = pobj.datatype(value)
                 except Exception as e:
                     err = e
-                    changed = False
                 else:
                     changed = pobj.value != value or pobj.readerror
                     # store the value even in case of error

test/test_modules.py

@@ -28,7 +28,7 @@ from glob import glob
 import pytest
 
 from frappy.datatypes import BoolType, FloatRange, StringType, IntRange, ScaledInteger
-from frappy.errors import ProgrammingError, ConfigError, RangeError
+from frappy.errors import ProgrammingError, ConfigError, RangeError, HardwareError
 from frappy.modules import Communicator, Drivable, Readable, Module, Writable
 from frappy.params import Command, Parameter, Limit
 from frappy.rwhandler import ReadHandler, WriteHandler, nopoll
@@ -941,3 +941,36 @@ def test_stop_doc(modcls):
     if (modcls.stop.description == Drivable.stop.description
             and modcls.stop.func != Drivable.stop.func):
         assert modcls.stop.func.__doc__  # stop method needs a doc string
+
+
+def test_write_error():
+    updates = {}
+    srv = ServerStub(updates)
+
+    class Mod(Module):
+        par = Parameter('', FloatRange(), readonly=False, default=0)
+
+        def read_par(self):
+            raise HardwareError('failure')
+
+        def write_par(self, value):
+            if value < 0:
+                raise RangeError('outside range')
+
+    a = Mod('a', LoggerStub(), {'description': 'test'}, srv)
+
+    # behaviour on read errors:
+    with pytest.raises(HardwareError):
+        a.read_par()
+    assert updates == {'a': {('error', 'par'): 'failure'}}
+    updates.clear()
+
+    # behaviour on normal write
+    a.write_par(1)
+    assert updates['a']['par'] == 1
+    updates.clear()
+
+    # behaviour when write failed
+    with pytest.raises(RangeError):
+        a.write_par(-1)
+    assert not updates # no error update!