Jest 30 isn't compatible with ts-jest 29, so I have downgraded the version in the packages where these were used together and it caused a problem. It seems there were a bit of a mix of 29/30 across different packages, so possibly the migration just triggered something in the affected packages.

ChatGPT analysis of what would be needed to upgrade:

I’ve mapped the migration surface: two packages are already split to Jest 29, the root base config and one generator package still carry ts-jest, and 23 package-level Jest configs still import the shared TS base config. I’m pulling the few key files behind that before I give you the cleanest Jest 30 path and cost.

To move entirely to Jest 30 in this repo, you need to remove the two things that are currently fighting it:

The first blocker is ts-jest. The shared root toolchain in package.json still pins ts-jest through catalog:test, and the shared config in jest.config.base.ts still uses preset: 'ts-jest' plus a ts-jest transform. That is the source of the clearMocksOnScope runtime failure when paired with Jest 30. You can either wait for a Jest 30-compatible ts-jest path you trust, or more realistically migrate off ts-jest entirely to a Jest 30-friendly transformer such as @swc/jest or babel-jest with TypeScript transpilation.

The second blocker is config loading. There are 23 package-level Jest configs still importing the shared TS base config, for example tests/pact-tests/jest.config.ts, src/python-schema-generator/jest.config.ts, and utils/utils/jest.config.ts. Jest 30 is less forgiving here because TS config loading goes through an ESM-sensitive path. You need one consistent strategy:

Convert the shared base config to plain JS or CJS and have package configs import that.
Or inline configs where needed, which src/typescript-schema-generator/jest.config.ts is already doing as a workaround.
Or keep TS configs but standardize the loader story with ts-node/ESM and verify every package works, which is the most fragile option.
If I were doing this cleanly, I would take this route:

Replace ts-jest in jest.config.base.ts with a Jest 30-compatible transform, likely @swc/jest.
Convert jest.config.base.ts to jest.config.base.cjs or jest.config.base.js.
Update all 23 package Jest configs to import that JS base config instead of TS.
Collapse the split catalogs back to one Jest 30 test catalog in pnpm-workspace.yaml.
Revalidate every package that runs tests, especially the two that already broke: src/cloudevents/package.json and tests/pact-tests/package.json.
In terms of effort, this is not a one-line dependency bump. It is a small migration:

Low-risk mechanical work: changing config files and imports.
Medium-risk work: changing the transformer and test runtime assumptions.
Main regression surface: path aliases, ESM/CJS handling, mock behavior, and coverage output.
The shortest safe path is not “upgrade Jest”; it is “replace ts-jest, convert shared config loading to JS, then upgrade everything together.”