def test_multiple_handlers_correctly_triggered():
sut = MessageBus()
sut.add_handler(MessageClassOne, get_one)
sut.add_handler(MessageClassOne, get_two)
sut.add_handler(MessageClassTwo, get_three)
message_one = MessageClassOne()
handling_result_one = sut.handle(message_one)
assert handling_result_one == [1, 2]
message_two = MessageClassTwo()
handling_result_two = sut.handle(message_two)
assert handling_result_two == [3]
def test_handler_is_triggered_each_time():
counter = 0
def handler(msg):
nonlocal counter
counter += 1
return counter
sut = MessageBus()
sut.add_handler(EmptyMessage, handler)
message = EmptyMessage()
handling_result = sut.handle(message)
assert handling_result == [1]
handling_result = sut.handle(message)
assert handling_result == [2]
def test_handlers_get_message():
sut = MessageBus()
sut.add_handler(EmptyMessage, identity_handler)
message = EmptyMessage()
handling_result = sut.handle(message)
assert handling_result == [message]
def test_simplest_handler():
sut = MessageBus()
sut.add_handler(EmptyMessage, get_one)
message = EmptyMessage()
handling_result = sut.handle(message)
assert handling_result == [1]
def test_multiple_handlers_for_single_message():
sut = MessageBus()
sut.add_handler(EmptyMessage, get_one)
sut.add_handler(EmptyMessage, get_one)
message = EmptyMessage()
handling_result = sut.handle(message)
assert handling_result == [1, 1]
def test_multiple_handlers_for_single_message_triggered_in_correct_order():
sut = MessageBus()
sut.add_handler(EmptyMessage, get_one)
sut.add_handler(EmptyMessage, get_two)
sut.add_handler(EmptyMessage, get_three)
message = EmptyMessage()
handling_result = sut.handle(message)
assert handling_result == [1, 2, 3]
class CommandBus(api.CommandBus):
def __init__(
self,
*,
middlewares: t.List[api.Middleware] = None,
allow_result: bool = True,
locking: bool = True,
) -> None:
self._messagebus = MessageBus(middlewares=middlewares)
self._allow_result = bool(allow_result)
self._locking = bool(locking)
self._is_processing_a_message = False
def add_handler(self, message_class: type,
message_handler: t.Callable) -> None:
if self._messagebus.has_handler_for(message_class):
raise api.CommandHandlerAlreadyRegisteredForAType(
f"A command handler is already registed for message class '{message_class}'."
)
self._messagebus.add_handler(message_class, message_handler)
def handle(self, message: object) -> t.Any:
if not self._messagebus.has_handler_for(message.__class__):
raise api.CommandHandlerNotFound(
f"No command handler is registered for message class '{message.__class__}'."
)
if self._locking and self._is_processing_a_message:
raise api.CommandBusAlreadyProcessingAMessage(
f"CommandBus already processing a message when received a '{message.__class__}' one." # pylint: disable=line-too-long
)
self._is_processing_a_message = True
result = self._messagebus.handle(message)
self._is_processing_a_message = False
return result[0] if self._allow_result else None
def has_handler_for(self, message_class: type) -> bool:
return self._messagebus.has_handler_for(message_class)
def test_simplest_handler_can_have_no_handlers_for_a_message():
sut = MessageBus()
message = EmptyMessage()
handling_result = sut.handle(message)
assert handling_result == []
def test_middlewares():
class MessageWithList(t.NamedTuple):
payload: t.List[str]
def middleware_one(message: MessageWithList, next: api.CallNextMiddleware):
message.payload.append(
"middleware one: does something before the handler")
result = next(message)
message.payload.append(
"middleware one: does something after the handler")
return result
def middleware_two(message: MessageWithList, next: api.CallNextMiddleware):
message.payload.append(
"middleware two: does something before the handler")
result = next(message)
message.payload.append(
"middleware two: does something after the handler")
return result
def handler_one(message: MessageWithList):
message.payload.append("handler one does something")
return "handler one result"
def handler_two(message: MessageWithList):
message.payload.append("handler two does something")
return "handler two result"
# 1. Simplest test: one handler, one middleware
sut1 = MessageBus(middlewares=[middleware_one])
sut1.add_handler(MessageWithList, handler_one)
message1 = MessageWithList(payload=[])
result1 = sut1.handle(message1)
assert result1 == ["handler one result"]
assert message1.payload == [
"middleware one: does something before the handler",
"handler one does something",
"middleware one: does something after the handler",
]
# 2. Next step: one handler, multiple middlewares
sut2 = MessageBus(middlewares=[middleware_one, middleware_two])
sut2.add_handler(MessageWithList, handler_one)
message2 = MessageWithList(payload=[])
result2 = sut2.handle(message2)
assert result2 == ["handler one result"]
assert message2.payload == [
"middleware one: does something before the handler",
"middleware two: does something before the handler",
"handler one does something",
"middleware two: does something after the handler",
"middleware one: does something after the handler",
]
# 3. Ultimate step: multiple handlers, multiple middlewares
sut3 = MessageBus(middlewares=[middleware_one, middleware_two])
sut3.add_handler(MessageWithList, handler_one)
sut3.add_handler(MessageWithList, handler_two)
message3 = MessageWithList(payload=["initial message payload"])
result3 = sut3.handle(message3)
assert result3 == ["handler one result", "handler two result"]
assert message3.payload == [
"initial message payload",
"middleware one: does something before the handler",
"middleware two: does something before the handler",
"handler one does something",
"handler two does something",
"middleware two: does something after the handler",
"middleware one: does something after the handler",
]