Added test case for decorators. Improved the 'mutate' decorator.

eventsourcing/domain/model/decorators.py

@@ -1,5 +1,7 @@
 from inspect import isfunction
 
+from six import wraps
+
 try:
     # Python 3.4+
     from functools import singledispatch
@@ -38,19 +40,35 @@ def wrap(handler_func):
     return wrap
 
 
-def mutator(func):
+def mutator(arg=None):
     """Like singledispatch, but dispatches on type of last arg,
     which fits better with reduce().
+
+    Can be used directly, invoked with the decorated
+    function. Can also be invoked with the type it
+    handles, to create a decorator that injects the type
+    when the given initial value is None.
     """
 
-    wrapped = singledispatch(func)
+    domain_class = None
+
+    def _mutator(func):
+        wrapped = singledispatch(func)
 
-    def wrapper(*args, **kw):
-        return wrapped.dispatch(args[-1].__class__)(*args, **kw)
+        @wraps(wrapped)
+        def wrapper(initial, event):
+            initial = initial or domain_class
+            return wrapped.dispatch(type(event))(initial, event)
 
-    wrapper.register = wrapped.register
+        wrapper.register = wrapped.register
 
-    return wrapper
+        return wrapper
+
+    if isfunction(arg):
+        return _mutator(arg)
+    else:
+        domain_class = arg
+        return _mutator
 
 
 def attribute(getter):

eventsourcing/tests/core_tests/test_aggregate_root.py

@@ -151,6 +151,9 @@ def id(self):
 
 @mutator
 def mutate_example_aggregate(self, event):
+    """
+    Mutator function for class ExampleAggregateRoot.
+    """
     return mutate_entity(self, event)
 
 

eventsourcing/tests/core_tests/test_decorators.py

@@ -0,0 +1,60 @@
+from unittest.case import TestCase
+
+from eventsourcing.domain.model.decorators import mutator
+
+
+class TestDecorators(TestCase):
+
+    def test_mutate_without_arg(self):
+        # Define an entity class, and event class, and a mutator function.
+
+        class Entity(object): pass
+
+        class Event(object): pass
+
+        @mutator
+        def mutate_entity(initial, event):
+            """Docstring for function mutate()."""
+            raise NotImplementedError()
+
+        # Check the function looks like the original.
+        self.assertEqual(mutate_entity.__doc__, "Docstring for function mutate().")
+
+        # Check it is capable of registering event handlers.
+        @mutate_entity.register(Event)
+        def mutate_with_event(initial, event):
+            return Entity()
+
+        # Check it dispatches on type of last arg.
+        self.assertIsInstance(mutate_entity(None, Event()), Entity)
+
+        # Check it handles unregistered types.
+        with self.assertRaises(NotImplementedError):
+            mutate_entity(None, None)
+
+    def test_mutate_with_arg(self):
+        # Define an entity class, and event class, and a mutator function.
+
+        class Entity(object): pass
+
+        class Event(object): pass
+
+        @mutator(Entity)
+        def mutate_entity(initial, event):
+            """Docstring for function mutate()."""
+            raise NotImplementedError()
+
+        # Check the function looks like the original.
+        self.assertEqual(mutate_entity.__doc__, "Docstring for function mutate().")
+
+        # Check it is capable of registering event handlers.
+        @mutate_entity.register(Event)
+        def mutate_with_event(initial, event):
+            return initial()
+
+        # Check it dispatches on type of last arg.
+        self.assertIsInstance(mutate_entity(None, Event()), Entity)
+
+        # Check it handles unregistered types.
+        with self.assertRaises(NotImplementedError):
+            mutate_entity(None, None)

eventsourcing/tests/core_tests/test_entity.py

@@ -220,6 +220,7 @@ def test_mutator_errors(self):
             created_mutator(TimestampedVersionedEntity, mock.Mock(spec=Created))  # needs more than the mock obj has
 
 
+
 class CustomValueObject(object):
     def __init__(self, value):
         self.value = value