[HUDI-7176] Add unit tests for log file only file slices

[linliu-code]

Change Logs

Base on PR: 10398.

Add unit test for log file only FileSlice: TestFileSliceWithOnlyLogFiles.java

Impact

Fixed problems.

Risk level (write none, low medium or high below)

LOW.

Contributor's checklist

• [ ] Read through contributor's guide
• [ ] Change Logs and Impact were stated clearly
• [ ] Adequate tests were added if applicable
• [ ] CI passed

[hudi-bot]

CI report:

• 7d4dbcfc15c3fd85abeb0d7ef2b853b9ed6cf77c Azure: FAILURE

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