wip add more unit tests

[hongyunyan]

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Issue Number: close #xxx

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Tests

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@hongyunyan: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-check	3a8b800	link	true	/test pull-check

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[gemini-code-assist]

Summary of Changes

Hello @hongyunyan, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly expands the unit test coverage across several core components, including the event dispatcher, MySQL sink, and barrier maintainer. The new tests validate critical behaviors such as sequential task execution for dispatchers, correct redo log gating for DML events, proper handling of DDLs in BDR mode, accurate barrier event forwarding, and the correct ordering of DDL and syncpoint barriers. Additionally, a test ensures DDL statements with unsupported VECTOR column types are correctly rewritten for downstream compatibility. These additions aim to bolster the system's robustness and ensure data consistency and replication integrity under various operational scenarios.

Highlights

• Dispatcher Task Serialization: Added a new unit test (TestBlockEventExecutorSerializesPerDispatcherTasks) to verify that tasks submitted for the same dispatcher are executed sequentially, ensuring block-event ordering guarantees.
• Redo Log Gating for Event Dispatcher: Introduced a new unit test (TestEventDispatcherRedoGating) to confirm that the event dispatcher correctly caches DML events with commitTs greater than redoGlobalTs, replaying them only when redoGlobalTs catches up, which is vital for downstream correctness and recovery.
• BDR Mode DDL Handling in MySQL Sink: Added a unit test (TestMysqlSinkWriteBlockEventSkipsNonPrimaryBDRRole) to ensure that in Bi-Directional Replication (BDR) mode, the MySQL sink skips executing non-primary-role DDLs but still triggers PostFlush to prevent upstream deadlocks.
• Barrier Event Forwarding Logic: A new unit test (TestForwardBarrierEvent) was added to validate the rules for forwarding barrier events based on a span replication's checkpoint and block state, preventing deadlocks and maintaining ordering guarantees.
• DDL and Syncpoint Barrier Ordering: Included a new unit test (TestPendingScheduleEventMapOrdersDDLBeforeSyncpointAtSameTs) to verify that the pendingScheduleEventMap correctly prioritizes DDL barriers over syncpoint barriers when they share the same commit timestamp.
• DDL Rewriting for Vector Column Types: A new unit test (TestFormatQueryRewritesVectorColumnType) was added to confirm that formatQuery in the MySQL sink rewrites unsupported VECTOR column definitions in DDL statements to compatible types (e.g., LONGTEXT or LONGBLOB), preventing DDL execution failures.

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[gemini-code-assist]

Code Review

This pull request adds a comprehensive set of unit tests across various packages, including dispatcher, sink, and maintainer. The new tests cover important logic and edge cases related to task serialization, redo log gating, BDR mode behavior, barrier event forwarding, and DDL handling. The tests are well-structured and include clear explanations of the scenarios they cover, which significantly improves the test coverage and maintainability of the codebase. My review includes one suggestion to make a test assertion more specific.

[gemini-code-assist]

The test assertion is a bit loose. The implementation in formatQuery specifically rewrites VECTOR to LONGBLOB. The test should assert for LONGBLOB specifically to be more precise and catch unintended changes. Checking for either LONGTEXT or LONGBLOB makes the test less effective if the desired behavior is strictly LONGBLOB.

require.Contains(t, upper, "LONGBLOB", "expected rewritten query to use LONGBLOB")