Test Sharding

Modern CI hosts offer multi-core environments that allow some degree of test parallelization. However, there are scenarios where you need to go beyond what a single host can offer — for example, when you're limited by the number of simulators you can run simultaneously, or when your test suite simply outgrows a single machine.

In those cases, you need a system that distributes tests across multiple CI runners and aggregates the results back into a unified view. That's what test sharding does.

Tuist uses historical test timing data to intelligently balance the load across shards using a bin-packing algorithm, so each runner finishes at roughly the same time. Results from all shards are automatically aggregated in Test Insights, giving you a single unified view of your test suite across all shards.