Add Unit Test

Workflow

1. Inspect the production code and the nearest existing tests before writing a new test.

   • Match the production path under xllm/ to tests/ where possible.
   • Prefer extending an existing nearby *_test.cpp and cc_test target when the behavior belongs to the same domain.
   • Create a new test source only when it improves isolation, keeps platform setup separate, or follows an existing directory pattern.

2. Read the project style guide before editing production files under xllm/, and apply the same C++ style discipline to new test code: .agents/skills/code-review/references/custom-code-style.md.

3. Follow the current test layout and CMake conventions.

   • Read xllm-test-patterns.md when adding a new test file, new cc_test, platform-specific test, or test directory.
   • Use *_test.cpp for C++ test files and *_test.cu for CUDA source tests.
   • Do not create nested test/ or tests/ directories for new unit tests unless the surrounding tree already requires that structure.