Jasmine -> Jest migration (WIP)

notes.md

Migration Steps

1. yarn add ts-jest jest @types/jest --dev
2. yarn remove jasmine jasmine-spec-reporter jasmine-ts ts-node proxyquire @types/jasmine @types/proxyquire
3. yarn ts-jest config:init
4. Modify jest.config.js if needed.
   • Add modulePathIgnorePatterns: ['.yarn-cache'] if there is a .yarn-cache folder; otherwise you'll get a lot of jest-haste-map errors when running tests.
5. Update the npm scripts. Give it the folder of tests you want to run (Jest matches against the pattern). Use --verbose to see the breakdown.
   • e.g. NODE_ENV=test jest test/unit --verbose
   • e.g. NODE_ENV=test jest test/unit --verbose --watch
6. (Experimental -- I haven't had much success with this) Try the migration tool: npx jest-codemods. (Run npm i -g npx if you don't have npx installed.)
7. Fix up tests
   • (probable) Update mocks to use Jest mocks.
     • Import what you're mocking and use jest.mock() on that same module. Use ts-jest's mocked() on the object to keep TSC from complaining.
     • See node-template's https://github.com/Banno/node-template/blob/master/test/integration/configure-logger.spec.ts for an example.
   • (optional) Replace jasmine.* references like jasmine.createSpy and jasmine.any to conform to the Jest API.

Tips

• One downside: We can't use fdescribe/fit to focus tests when running against multiple tests -- Jest runs each file separately. Modify the Jest CLI call instead (e.g. jest test/unit/example.spec.ts).
• To see the compiled JS for the tests, run jest --debug to find the cache dir, then look in that (inside the ts-jest folder).
• If you get A "describe" callback must not return a value and there are only statements inside a describe, check that an error isn't being thrown in there. In general, it's safest to put all that code in beforeAll/beforeEach blocks.