Lack test for Rangesplitter

[shiyuhang0]

Bug Report

1. Describe the bug

Client-java lack test for Rangesplitter

2. Minimal reproduce step (Required)

3. What did you see instead (Required)

4. What did you expect to see? (Required)

5. What are your Java Client and TiKV versions? (Required)

• Client Java:
• TiKV: