Send module build state change message after commit to database

In MBS, there are two cases to send a message when a module build moves
to a new state. One is to create a new module build, with
ModuleBuild.create particularly, when user submit a module build.
Another one is to transition a module build to a new state with
ModuleBuild.transition. This commit handles these two cases in a little
different ways.

For the former, existing code is refactored by moving the publish call
outside ModuleBuild.create.

For the latter, message is sent in a hook of SQLAlchemy ORM event
after_commit rather than immediately inside the ModuleBuild.transition.

Both of these changes ensure the message is sent after the changes are
committed into database successfully. Then, the backend can have
confidence that the database has the module build data when receive a
message.

Signed-off-by: Chenxiong Qi <cqi@redhat.com>

tests/test_scheduler/test_db_session.py

@@ -0,0 +1,27 @@
+# -*- coding: utf-8 -*-
+# SPDX-License-Identifier: MIT
+
+from mock import patch
+
+from module_build_service import conf
+from module_build_service.common import models
+from module_build_service.scheduler.db_session import db_session
+from tests import clean_database, make_module_in_db
+
+
+@patch('module_build_service.common.messaging.publish')
+def test_send_messages_after_several_state_transitions(mock_publish):
+    """
+    Ensure all module build state change messages are sent after multiple
+    ModuleBuild.transitions are committed at once
+    """
+    clean_database()
+
+    build = make_module_in_db("testmodule:1:2:c3")
+
+    build.transition(db_session, conf, models.BUILD_STATES["wait"])
+    build.transition(db_session, conf, models.BUILD_STATES["done"])
+
+    assert 0 == mock_publish.call_count
+    db_session.commit()
+    assert 2 == mock_publish.call_count

tests/test_scheduler/test_greenwave_handler.py

@@ -138,10 +138,10 @@ class TestDecisionUpdateHandler:
 
         # Assert this call below
         first_publish_call = call(
-            service="mbs",
-            topic="module.state.change",
-            msg=module_build.json(db_session, show_tasks=False),
-            conf=conf,
+            "module.state.change",
+            module_build.json(db_session, show_tasks=False),
+            conf,
+            "mbs",
         )
 
         ClientSession.return_value.getBuild.return_value = {
@@ -169,9 +169,9 @@ class TestDecisionUpdateHandler:
         publish.assert_has_calls([
             first_publish_call,
             call(
-                service="mbs",
-                topic="module.state.change",
-                msg=module_build.json(db_session, show_tasks=False),
-                conf=conf,
+                "module.state.change",
+                module_build.json(db_session, show_tasks=False),
+                conf,
+                "mbs"
             ),
         ])