Running typescript jest tests with bun

[robobun]

Hi there!

Trying to migrate our codebase to bun. Sadly we can't use the built in bun test runner as we need to use mocks, which are currently unsupported. Our current test setup is jest, using the ts-jest preset in order to run them

As part of the initial configuration with bun, we updated our tsconfig, from:

{
  "compilerOptions": {
    "module": "commonjs",
    "target": "es2022",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,
    "allowSyntheticDefaultImports": true,
    "outDir": "dist",
    "moduleResolution": "node",
    "sourceMap": true
  },
  "compileOnSave": true,
  "include": ["src/**/*.ts"],
  "exclude": ["node_modules"],
}

to

{
  "compilerOptions": {
    "lib": ["ESNext"],
    "module": "esnext",
    "target": "esnext",
    "moduleResolution": "bundler",
    "moduleDetection": "force",
    "allowImportingTsExtensions": true,
    "noEmit": true,
    "composite": true,
    "strict": true,
    "downlevelIteration": true,
    "skipLibCheck": true,
    "jsx": "preserve",
    "allowSyntheticDefaultImports": true,
    "forceConsistentCasingInFileNames": true,
    "allowJs": true,
    "types": [
      "bun-types" // add Bun global
    ]
  }
}

However, with this updated tsconfig, both bun run test and npm run test now fail, as every import resolves to undefined, so code like this in test files fails

import { jsdom } from 'jsdom'
jsdom.JSDOM

as jsdom is undefined

Originally reported on Discord: Running typescript jest tests with bun

[Wazbat]

Created example repo: https://github.com/Wazbat/bun-ts-jest-example