jest test.each types not matching: typescript fix

TL;DR

test.each infers row types from the table, and the inference often comes out wider or narrower than your callback expects, especially with mixed-type rows or template-literal tables. The reliable fix is to type the table explicitly: use as const on array tables, or annotate the callback parameters, so the row type and the callback signature agree. When the table has heterogeneous rows, type it as a tuple union instead of letting inference widen everything to string | number.

The query

jest test.each types not matching: typescript fix

Use this when

• TypeScript errors inside test.each callbacks about argument types
• Template-literal tables (test.each\...\`) giving string` where you need numbers
• Refactoring a test table breaks type checking but tests still run

Not for

• Runtime failures in parameterized tests
• Plain JavaScript test.each usage
• Jest type errors outside test.each

Steps

1. Read the exact TS error on the callback parameters and compare with the inferred table row type (hover the table in your editor). Expected output: you see the mismatch, e.g. rows inferred as (string | number)[] while the callback wants [string, number].
2. Type the table explicitly: add as const to array tables, or declare the row tuple type and annotate the table with it. Expected output: the table's inferred type now matches the callback signature.
3. For template-literal tables, convert values at the row level or switch to an array table when you need non-string types. Expected output: numeric/boolean columns keep their types instead of widening to string.
4. Run tsc --noEmit (or your typecheck) and then the tests. Expected output: type errors gone, tests still green.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_G6fahn8oCYoP1lDtBmDNiw