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Testing / Playwright Interview questions

What is the difference between sharding and parallel workers in Playwright?

Both spread work out for speed, but at different levels - one within a single machine, the other across multiple machines entirely.

Parallel workersSharding
Multiple processes on one machineSplitting the whole suite across separate machines/CI jobs
Configured via workers in configConfigured via --shard=index/total CLI flag
Limited by that machine's CPU coresLimited only by how many CI runners you provision

In practice they're combined: a CI pipeline might run 4 shards (--shard=1/4 through 4/4) on 4 separate runners, and each of those runners then also runs several parallel workers internally. Sharding is what lets a suite scale past the ceiling of a single machine's CPU count, which workers alone can't do.

Because each shard produces its own separate report, merging them into one combined HTML report afterward typically uses the blob reporter per shard followed by a merge-reports step, rather than trying to stitch plain HTML output back together manually.

Sharding differs from parallel workers mainly because it:
A typical CI setup combines the two by:

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