ddl: refine test TestDDLJobErrorCount and remove test TestBackwardCompatibility

[wjhuang2016]

Signed-off-by: wjhuang2016 huangwenjun1997@gmail.com

What problem does this PR solve?

Issue Number: ref #33008

Problem Summary:

1. For TestDDLJobErrorCount, do DDL by SQL statement.
2. For TestBackwardCompatibility, it tests the upgrading from 2.0. Since 2.0 is not supported anymore, I think it's ok to remove it. It uses EnQueueDDLJob which would break the new DDL framework.

What is changed and how it works?

As title.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• hawkingrei
• xiongjiwei

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[xiongjiwei]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 2371ecd

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Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/160444ebf81c9cb4895a6792d213853fb8ae857c