CI/CD & Pipelines
Test Split Calculator
Enter test suite duration, target shard duration, and setup time to compute optimal shard count, expected wall-clock time, and parallel efficiency.
No data is transmitted — everything runs locallyTool
Example — 90-min suite · 15-min shard target · 2-min setup
Optimal shards
6
ceil(90÷15)
Wall-clock time
17.0 min
shard + setup overhead
Time saved
73.0 min
vs serial execution
Parallelism efficiency
81.1%
diminishes with setup overhead
About this tool
Test Split Calculator
The Test Split Calculator computes optimal shard count, wall-clock time, and parallel efficiency from test suite duration, target shard time, and per-shard setup overhead.
• Determine optimal shard count before configuring pytest-split or jest --shard
• Calculate whether adding more shards will still reduce wall time given setup overhead
• Model wall-clock time reduction from splitting a 45-minute test suite
• Identify when setup time dominates and sharding is no longer beneficial
Affiliate disclosure
Uptime, incident, and on-call management. Better Stack provides status pages, incident management, and on-call scheduling for engineering teams.
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FAQ
What does this tool tell you?
The Test Split Calculator computes optimal shard count, wall-clock time, and parallel efficiency from test suite duration, target shard time, and per-shard setup overhead.
What affects the result most?
Optimal shards = ceil(test_suite_duration / target_shard_duration). Test distribution: uniform split by count vs time-based split — time-based produces even wall time. Shard overhead: each shard has startup cost (container spin, dependency install) ~2-3 min.
How should I use the result?
The calculation is deterministic — the same inputs always produce the same output — so the most useful workflow is to vary one input at a time and see which factor moves the result most. That tells you where to focus your attention before committing to a decision.
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