Engineering notes on warm test runs, Jest compatibility, and benchmark methodology from the rjest team at Neullabs.https://rjest.neullabs.com/en-ushttps://rjest.neullabs.com/blog/how-we-benchmarked-methodology/https://rjest.neullabs.com/blog/how-we-benchmarked-methodology/The 100x number in the README is from a specific workload, on a specific machine, with a specific definition of cold and warm. This post explains exactly what we measured, where the speedup is largest, where it shrinks, and what would be misleading to report.Tue, 26 May 2026 00:00:00 GMThttps://rjest.neullabs.com/blog/drop-in-compatibility-contract/https://rjest.neullabs.com/blog/drop-in-compatibility-contract/rjest's only interesting feature for the first hour is that it does not break anything. We explain the compatibility contract — config, CLI, matchers, mocks, output shape — and why we treat any deviation as a bug we have to fix, not a tradeoff we get to negotiate.Tue, 19 May 2026 00:00:00 GMThttps://rjest.neullabs.com/blog/why-warm-jest-runs-are-slow/https://rjest.neullabs.com/blog/why-warm-jest-runs-are-slow/On a real codebase, the time Jest takes between npx jest and the first PASS rarely has anything to do with assertions. We break down the hidden cost — config, transform, worker boot, JIT — and explain where rjest amortizes each one.Tue, 12 May 2026 00:00:00 GMT