#shard

• Type: { count: number; index: number }
• Default: undefined
• CLI: --shard <index>/<count>

Shards test files for parallel execution. count represents the total number of shards, and index represents the index of the current shard (1-based).

This option can only be set at the root level of your configuration, not within individual projects.

This is particularly useful for parallelizing tests in CI/CD environments, allowing you to split the test suite into multiple parts and run them independently across different jobs, thereby reducing overall test time.

# Split tests into 3 shards, run the 1st shard
npx rstest --shard 1/3

import { defineConfig } from '@rstest/core';

export default defineConfig({
  shard: {
    count: 3,
    index: 1,
  },
});

#Merging shard reports

When using sharding in CI, each shard produces its own test report and coverage data independently. To combine the results from all shards into a single report, use the blob reporter along with the rstest merge-reports command.

#Step 1: run shards with blob reporter

Configure each shard to output results using the blob reporter:

# Shard 1
npx rstest run --shard 1/3 --reporter=blob --coverage

# Shard 2
npx rstest run --shard 2/3 --reporter=blob --coverage

# Shard 3
npx rstest run --shard 3/3 --reporter=blob --coverage

Each shard writes its results to .rstest-reports/blob-{index}-{count}.json.

#Step 2: merge reports

After all shards complete, collect all blob files into a single .rstest-reports/ directory and run:

npx rstest merge-reports --cleanup

This will merge all test results, generate a unified summary using your configured reporters, and combine coverage data.

See the CLI documentation for more details on the merge-reports command.