docs: revise style guide about test mod

Signed-off-by: Ruihang Xia <[email protected]>

CONTRIBUTING.md

@@ -50,7 +50,7 @@ GreptimeDB uses the [Apache 2.0 license](https://github.com/GreptimeTeam/greptim
 
 - To ensure that community is free and confident in its ability to use your contributions, please sign the Contributor License Agreement (CLA) which will be incorporated in the pull request process.
 - Make sure all files have proper license header (running `docker run --rm -v $(pwd):/github/workspace ghcr.io/korandoru/hawkeye-native:v3 format` from the project root).
-- Make sure all your codes are formatted and follow the [coding style](https://pingcap.github.io/style-guide/rust/) and [style guide](http://github.com/greptimeTeam/docs/style-guide.md).
+- Make sure all your codes are formatted and follow the [coding style](https://pingcap.github.io/style-guide/rust/) and [style guide](https://github.com/GreptimeTeam/greptimedb/blob/main/docs/style-guide.md).
 - Make sure all unit tests are passed (using `cargo test --workspace` or [nextest](https://nexte.st/index.html) `cargo nextest run`).
 - Make sure all clippy warnings are fixed (you can check it locally by running `cargo clippy --workspace --all-targets -- -D warnings`).
 

docs/style-guide.md

@@ -12,7 +12,7 @@ It's mainly an complement to the [Rust Style Guide](https://pingcap.github.io/st
 
 ## Formatting
 
-- Place all `mod` declaration before any `use`.
+- Place all `mod` declaration before any `use` (except the test mod).
 - Use `unimplemented!()` instead of `todo!()` for things that aren't likely to be implemented.
 - Add an empty line before and after declaration blocks.
 - Place comment before attributes (`#[]`) and derive (`#[derive]`).