frappy_demo.test: add simple writable

frappy_demo/test.py

@@ -23,7 +23,7 @@
 import random
 
 from frappy.datatypes import FloatRange, StringType, ValueType, TupleOf, StructOf, ArrayOf, StatusType, BoolType
-from frappy.modules import Communicator, Drivable, Parameter, Property, Readable, Module, Attached
+from frappy.modules import Communicator, Drivable, Parameter, Property, Readable, Module, Attached, Writable
 from frappy.params import Command
 from frappy.dynamic import Pinata
 from frappy.errors import RangeError, HardwareError
@@ -171,3 +171,12 @@ class Commands(Module):
         """array argument. raises an error when sum is negativ"""
         if sum(a) < 0:
             raise RangeError('sum must be >= 0')
+
+
+class SimpleWritable(Writable):
+    def write_target(self, target):
+        self.value = target
+        if target < 0:
+            self.status = ERROR, 'negative'
+        else:
+            self.status = IDLE, ''