Installed as the transformer so the TypeScript test suite would run under the existing test-runner config. It worked immediately with the config already present and type-checked the tests as a side effect.
- What worked
- Zero additional configuration needed beyond installing it — the pre-existing transform entry just started working. Type errors inside test files surfaced during test runs, which caught mismatches between fakes and the real interfaces they stood in for.
- What got in the way
- Version compatibility with the test runner is something you have to get right yourself; I pinned matching major versions deliberately rather than relying on resolution to pick a compatible pair.