Fix assert_expected_events macro in xcm_emulator

[ParthDesai]

Description

This PR aims to fix assert_expected_events by only setting meet_conditions variable when we detect a matching event and have evaluated all conditions specified by user. This fixes an issue where assert_expected_events will not panic in case our event is not the last event in the Chain::System::events() vector.

Context

assert_expected_events first fetch events emitted by runtime lets call it system_events ; It also intializes message variable as vector of string that contains the panic message. For every event user_event we declared in the vec! along with conditions, it does following:

1. Declare match_conditions variable with initial value of true.
2. Start for loop to iterate through system_events. For each system event, it does following in the for loop block:
   a. re-initialize match_conditions to true // <-- This is the bug, it simply over-writes past conditions match failures without checking current event matches user_event and also without evaluating any conditions.
   b. if match is found, it tries to check if conditions are satisfied, if any one of the condition is not satisfied meet_conditions variable is set to false.
3. If meet_conditions is false and we received the event, it pushes an error string in message vector.

[paritytech-cicd-pr]

The CI pipeline was cancelled due to failure one of the required jobs.
Job name: test-linux-stable 3/3
Logs: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/6066962

[acatangiu]

Can you add a unit-test showcasing the fixed scenario? A regression test that fails without your fix and passes with it. It will also help reviewers better understand the problem.

[ParthDesai]

Can you add a unit-test showcasing the fixed scenario? A regression test that fails without your fix and passes with it. It will also help reviewers better understand the problem.

Tried to write unit test, but problem is the macro expects implementation of Chain trait and I could not find a test/mock implementation of Chain trait in which I can inject some system event and then call this macro. Can you point me to right direction here?

[liamaharon]

test? I see above review already mentioned this, taking a look

[franciscoaguirre]

@ParthDesai It's true we don't have a special emulated chain for these types of things, it should probably go in the xcm-emulator.
You could create an emulated chain as a mock to test this, like the ones we have in cumulus/parachains/integration-tests/emulated/chains/relays/westend/src/lib.rs