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Try to teach CoPi a bit about how we'd like to see it implement tests, according to this repo best practices. Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com> Closes scylladb/scylladb#28032
98 lines
4.3 KiB
Markdown
98 lines
4.3 KiB
Markdown
# ScyllaDB Development Instructions
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## Project Context
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High-performance distributed NoSQL database. Core values: performance, correctness, readability.
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## Build System
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### Modern Build (configure.py + ninja)
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```bash
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# Configure (run once per mode, or when switching modes)
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./configure.py --mode=<mode> # mode: dev, debug, release, sanitize
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# Build everything
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ninja <mode>-build # e.g., ninja dev-build
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# Build Scylla binary only (sufficient for Python integration tests)
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ninja build/<mode>/scylla
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# Build specific test
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ninja build/<mode>/test/boost/<test_name>
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```
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## Running Tests
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### C++ Unit Tests
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```bash
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# Run all tests in a file
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./test.py --mode=<mode> test/<suite>/<test_name>.cc
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# Run a single test case from a file
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./test.py --mode=<mode> test/<suite>/<test_name>.cc::<test_case_name>
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# Examples
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./test.py --mode=dev test/boost/memtable_test.cc
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./test.py --mode=dev test/raft/raft_server_test.cc::test_check_abort_on_client_api
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```
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**Important:**
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- Use full path with `.cc` extension (e.g., `test/boost/test_name.cc`, not `boost/test_name`)
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- To run a single test case, append `::<test_case_name>` to the file path
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- If you encounter permission issues with cgroup metric gathering, add `--no-gather-metrics` flag
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**Rebuilding Tests:**
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- test.py does NOT automatically rebuild when test source files are modified
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- Many tests are part of composite binaries (e.g., `combined_tests` in test/boost contains multiple test files)
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- To find which binary contains a test, check `configure.py` in the repository root (primary source) or `test/<suite>/CMakeLists.txt`
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- To rebuild a specific test binary: `ninja build/<mode>/test/<suite>/<binary_name>`
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- Examples:
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- `ninja build/dev/test/boost/combined_tests` (contains group0_voter_calculator_test.cc and others)
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- `ninja build/dev/test/raft/replication_test` (standalone Raft test)
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### Python Integration Tests
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```bash
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# Only requires Scylla binary (full build usually not needed)
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ninja build/<mode>/scylla
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# Run all tests in a file
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./test.py --mode=<mode> <test_path>
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# Run a single test case from a file
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./test.py --mode=<mode> <test_path>::<test_function_name>
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# Examples
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./test.py --mode=dev alternator/
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./test.py --mode=dev cluster/test_raft_voters::test_raft_limited_voters_retain_coordinator
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# Optional flags
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./test.py --mode=dev cluster/test_raft_no_quorum -v # Verbose output
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./test.py --mode=dev cluster/test_raft_no_quorum --repeat 5 # Repeat test 5 times
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```
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**Important:**
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- Use path without `.py` extension (e.g., `cluster/test_raft_no_quorum`, not `cluster/test_raft_no_quorum.py`)
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- To run a single test case, append `::<test_function_name>` to the file path
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- Add `-v` for verbose output
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- Add `--repeat <num>` to repeat a test multiple times
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- After modifying C++ source files, only rebuild the Scylla binary for Python tests - building the entire repository is unnecessary
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## Code Philosophy
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- Performance matters in hot paths (data read/write, inner loops)
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- Self-documenting code through clear naming
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- Comments explain "why", not "what"
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- Prefer standard library over custom implementations
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- Strive for simplicity and clarity, add complexity only when clearly justified
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- Question requests: don't blindly implement requests - evaluate trade-offs, identify issues, and suggest better alternatives when appropriate
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- Consider different approaches, weigh pros and cons, and recommend the best fit for the specific context
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## Test Philosophy
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- Performance matters. Tests should run as quickly as possible. Sleeps in the code are highly discouraged and should be avoided, to reduce run time and flakiness.
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- Stability matters. Tests should be stable. New tests should be executed 100 times at least to ensure they pass 100 out of 100 times. (use --repeat 100 --max-failures 1 when running it)
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- Unit tests should ideally test one thing and one thing only.
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- Tests for bug fixes should run before the fix - and show the failure and after the fix - and show they now pass.
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- Tests for bug fixes should have in their comments which bug fixes (GitHub or JIRA issue) they test.
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- Tests in debug are always slower, so if needed, reduce number of iterations, rows, data used, cycles, etc. in debug mode.
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- Tests should strive to be repeatable, and not use random input that will make their results unpredictable.
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- Tests should consume as little resources as possible. Prefer running tests on a single node if it is sufficient, for example.
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