Change StubBroker.join() parameter fail_fast to default to True

Resolves #739

Author: LincolnPuzey

docs/source/guide.rst

@@ -490,17 +490,18 @@ synchronously by calling them as you would normal functions.
 Dealing with Exceptions
 ^^^^^^^^^^^^^^^^^^^^^^^^
 
-By default, any exceptions raised by an actor are raised in the
+By default, any exceptions raised by an actor are caught by the
 worker, which runs in a separate thread from the one your tests run
 in.  This means that any exceptions your actor throws will not be
-visible to your test code!
+immediately visible to your test code!
 
-You can make the stub broker re-raise exceptions from failed actors in your
-main thread by passing ``fail_fast=True`` to its ``join`` method::
+To help surface actor exceptions, by default,
+the stub broker will re-raise exceptions from failed messages
+in your main thread when you call its |StubBroker_join| method::
 
   def test_count_words(stub_broker, stub_worker):
-      count_words.send("http://example.com")
-      stub_broker.join(count_words.queue_name, fail_fast=True)
+      count_words.send("http://some-invalid-url.invalid")
+      stub_broker.join(count_words.queue_name)  # Exception from actor will be re-raised here.
       stub_worker.join()
 
 This way, whatever exception caused the actor to fail will be raised

docs/source/troubleshooting.rst

@@ -58,7 +58,12 @@ pytest_, then you can easily do this from the command line using the
 
 You can also pass ``fail_fast=True`` as a parameter to |StubBroker_join|
 in order to make it reraise whatever exception caused the actor to
-fail in the main thread.  Note, however, that the actor is only
+fail in the main thread.
+
+.. versionchanged:: 2.0.0
+   The ``fail_fast`` parameter now defaults to True.
+
+Note, however, that the actor is only
 considered to fail once all of its retries have been used up; meaning
 that unless you specify custom retry limits for the actors or for your
 tests as a whole (by configuring the |Retries| middleware), then each

dramatiq/brokers/stub.py

@@ -131,8 +131,7 @@ def flush_all(self) -> None:
 
         self.dead_letters_by_queue.clear()
 
-    # TODO: Make fail_fast default to True.
-    def join(self, queue_name: str, *, timeout: Optional[int] = None, fail_fast: bool = False) -> None:
+    def join(self, queue_name: str, *, timeout: Optional[int] = None, fail_fast: bool = True) -> None:
         """Wait for all the messages on the given queue to be
         processed.  This method is only meant to be used in tests
         to wait for all the messages in a queue to be processed.
@@ -145,10 +144,13 @@ def join(self, queue_name: str, *, timeout: Optional[int] = None, fail_fast: boo
           queue_name(str): The queue to wait on.
           fail_fast(bool): When this is True and any message gets
             dead-lettered during the join, then an exception will be
-            raised.  This will be True by default starting with
-            version 2.0.
+            raised. When False, no exception will be raised.
+            Defaults to True.
           timeout(Optional[int]): The max amount of time, in
             milliseconds, to wait on this queue.
+
+        .. versionchanged:: 2.0.0
+           The ``fail_fast`` parameter now defaults to True.
         """
         try:
             queues = [