https://github.com/evanw/jest-esbuild-demo
https://github.com/evanw/jest-esbuild-demo
Last synced: about 2 months ago
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- Host: GitHub
- URL: https://github.com/evanw/jest-esbuild-demo
- Owner: evanw
- Created: 2021-02-16T09:36:10.000Z (over 4 years ago)
- Default Branch: master
- Last Pushed: 2021-02-16T09:36:25.000Z (over 4 years ago)
- Last Synced: 2025-04-11T00:12:52.312Z (about 2 months ago)
- Language: JavaScript
- Size: 92.8 KB
- Stars: 13
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# Jest + esbuild demo
_This repo was created as an example for a discussion in this thread: https://github.com/evanw/esbuild/issues/412._
This repo demonstrates that running Jest on the original source code is equivalent to running Jest on the source code bundled with esbuild. Since Jest's `spyOn` function works with CommonJS but doesn't work with ESM, running Jest on the code after bundling it with esbuild also works with CommonJS but doesn't work with ESM. This is because esbuild intentionally matches node's behavior.
## CommonJS
Jest's `spyOn` function works with node's CommonJS support, so it also works with esbuild's CommonJS support:
```sh
$ npm ci
$ npm run test:cjs
> test:cjs
> npm run build:cjs; cd ./cjs; node ../node_modules/.bin/jest
> build:cjs
> ./node_modules/.bin/esbuild --bundle ./cjs/__tests__/original.js --format=cjs --outfile=./cjs/__tests__/compiled.js
PASS __tests__/original.js
PASS __tests__/compiled.js
Test Suites: 2 passed, 2 total
Tests: 2 passed, 2 total
Snapshots: 0 total
Time: 0.828 s, estimated 1 s
Ran all test suites.
```
## ESM
Jest's `spyOn` function doesn't work with node's ESM support, so it also doesn't work with esbuild's ESM support:
```sh
$ npm ci
$ npm run test:esm
> test:esm
> npm run build:esm; cd ./esm; node --experimental-vm-modules ../node_modules/.bin/jest
> build:esm
> ./node_modules/.bin/esbuild --bundle ./esm/__tests__/original.js --format=esm --outfile=./esm/__tests__/compiled.js --external:@jest/globals
(node:35164) ExperimentalWarning: VM Modules is an experimental feature. This feature could change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
FAIL __tests__/original.js
● spyOn
TypeError: object.hasOwnProperty is not a function
4 | test("spyOn", () => {
5 | expect(sut.foo()).toEqual("foo");
> 6 | jest.spyOn(sut, "foo").mockReturnValue("bar");
| ^
7 | expect(sut.foo()).toEqual("bar");
8 | });
9 |
at ModuleMockerClass.spyOn (../node_modules/jest-mock/build/index.js:801:36)
at Object. (__tests__/original.js:6:8)
FAIL __tests__/compiled.js
● spyOn
TypeError: Cannot redefine property: foo
at Function.defineProperty ()
18 | test("spyOn", () => {
19 | expect(foo()).toEqual("foo");
> 20 | jest.spyOn(sut_exports, "foo").mockReturnValue("bar");
| ^
21 | expect(foo()).toEqual("bar");
22 | });
23 |
at ModuleMockerClass.spyOn (../node_modules/jest-mock/build/index.js:826:16)
at Object. (__tests__/compiled.js:20:8)
Test Suites: 2 failed, 2 total
Tests: 2 failed, 2 total
Snapshots: 0 total
Time: 0.848 s, estimated 1 s
Ran all test suites.
```