CLI Sharding Cheat-Sheet

Run tests in parallel across multiple processes to speed up large test suites:

Basic Sharding Commands

# Run 4 shards, this is shard 0 (of 0-3)t --shards 4 --shard-id 0# Run shard 1t --shards 4 --shard-id 1# Run shard 2t --shards 4 --shard-id 2# Run shard 3t --shards 4 --shard-id 3

Tests are distributed deterministically using a hash of the test file path, ensuring each test always runs in the same shard.

Combine with Other Flags

# Run with production mode (no coverage)t -p --shards 4 --shard-id 2# Add verbose outputt -l --shards 4 --shard-id 1# Custom worker countt --shards 4 --shard-id 0 --workers 2

Package.json for CI/CD

Add these scripts to your package.json:

{  "scripts": {    "test": "t -p",    "test:shard:0": "t -p --shards 4 --shard-id 0",    "test:shard:1": "t -p --shards 4 --shard-id 1",    "test:shard:2": "t -p --shards 4 --shard-id 2",    "test:shard:3": "t -p --shards 4 --shard-id 3"  }}

Run All Shards in Parallel

Use a single command to run all shards in parallel:

# Run all 4 shards in parallel and wait for all to completenpm run test:shard:0 & npm run test:shard:1 & npm run test:shard:2 & npm run test:shard:3 & wait

Or with production mode:

npm run test:shard:0 & npm run test:shard:1 & npm run test:shard:2 & npm run test:shard:3 & wait

Deterministic Distribution

Test distribution is deterministic - the same test file will always run in the same shard. This ensures consistent behavior across CI runs.