Sharding and merge-reports

This page shows how to collect UI coverage from sharded runs and merge it into one report with npx playwright merge-reports.

Coverage data and screenshots are stored as test attachments, so they travel with Playwright's blob reporter. Run each shard with the blob reporter, then merge on any machine with the UI coverage reporter:

# on each CI job
npx playwright test --shard=1/2 --reporter=blob
npx playwright test --shard=2/2 --reporter=blob

# after collecting every blob-report/*.zip into all-blob-reports/
npx playwright merge-reports --reporter playwright-ui-coverage/reporter all-blob-reports

The merged report is the same as one from an unsharded run.

Config when merging

The reporter finds ui-coverage.config.* next to the config merge-reports uses (with --reporter alone and no --config, that's the working directory), or through UI_COVERAGE_CONFIG.

Options set inline in playwright.config.ts aren't seen by merge-reports. Pass them in a merge config:

// merge.config.ts
export default {
  reporter: [['playwright-ui-coverage/reporter', { configFile: './ui-coverage.config.ts', threshold: 30 }]],
};

npx playwright merge-reports --config merge.config.ts all-blob-reports

To keep links from "Tested by" to Playwright's HTML report, put both reporters in the merge config; with --reporter html,playwright-ui-coverage/reporter on the command line the reporter can't see the HTML reporter's options, so there are no links. See Insights and the HTML report.

Recording in the shards

The shards record with the config file too: recording, and a profile selected by each test's project and tags, or by UI_COVERAGE_PROFILE. (When the run has no UI coverage reporter, as with --reporter=blob, each test selects the profile itself.)

In CI

For a GitHub Actions setup with shards, do the baseline, comparison and comment steps in the merge job, with baseline and githubSummary in the merge config's reporter options. See GitHub Actions workflow.