refactor `sql_cmd_test` & `mini_cluster`

the overall structure of `sql_cmd_test` & `mini_cluster` is a mess, mix of global variables and reference over different test case.

It's hard to maintain and add new test case easily

The issue points to sql_cmd_test and mini_cluster files, likely in a test directory. Start by examining the current structure, global variables, and cross-references between test cases. Understand how tests interact with the mini_cluster. Refactoring involves cleaning up dependencies and improving modularity. Verify changes by running existing tests to ensure they still pass.

Written by the indexing model from the issue text.