quorum
Raft consensus written from scratch, behind a linearizable key-value store.
Problem
Consensus is the piece most teams import rather than understand, and its failure modes only show up under partition, reorder and crash. Testing it is the harder half: a real cluster is slow, non-deterministic, and rarely reproduces the bug being chased.
Approach
The Raft core is written as a pure function. It never reads a clock, opens a socket or touches disk; it takes a message and the current time and returns new state plus outgoing messages, and a test enforces that purity. Every bit of I/O lives in a separate driver, which is what lets an entire cluster run inside one process under a seeded scheduler that can delay, drop, reorder and partition at will.
Outcome
147 tests run a real cluster in-process in about 25 seconds, asserting all four safety properties continuously. A Jepsen-style linearizability checker replays roughly 22,000 operations across chaos scenarios with zero violations, and all four negative controls are flagged as expected. Re-election settles at p50 235ms and p95 430ms against a 150 to 300ms election timeout.