Jest continues after running TypeScript single tests and increasing coverage

Cannot use import statement outside a module

Jest itself supports ESM, that is, a single test can be written this way

// src/lib/lite-lodash.js

export isPromise(.){... }Copy the code
// test/lib/lite-lodash.test.js

import { isPromise } from '.. /.. /src/lib/lite-lodash'

describe(...)
Copy the code

An error is reported when lite-lodash.js says import XX from YY. In fact, Babel does not recognize the import of the file under test.

Cannot use import statement outside a module

solution

Step 1: Install Babel-Jest

Step 2: Touch babel.config.js

// Only used by Jest should not affect business code building!
module.exports = { presets: ['@babel/preset-env']};Copy the code

Step 3: jest.config.js

module.exports = {
  transform: {
    "^.+\\.(js|jsx)$": "babel-jest",}};Copy the code

alias

The config file alias alis can solve the problem of import requiring the mental calculation of the path, we often use in Webpack or TS development experience optimization measures, such as

// jsconfig.json

{
  "compilerOptions": {
    "checkJs": true."target": "es2015"."moduleResolution": "node"."resolveJsonModule": true."baseUrl": "."."paths": {
      "@ / *": ["./src/*"]}},"exclude": ["dist"."node_modules"."**/node_modules/*"]}Copy the code

But the trouble is if the file you test contains

import '@/common/lib/xxx'
Copy the code

Jest complains that it can’t find the file

Cannot find module ‘@/common/tools/format’ from ‘test/common/tools/url.test.js’

solution

jest.config.js

+ 'moduleNameMapper': {
+ '^@/(.*)': '
      
       /src/$1',
      
+},
Copy the code

Cannot read property ‘cwd’ of undefined

Jest error:

Test suite failed to run

TypeError: Cannot read property ‘cwd’ of undefined

at Object.process (node_modules/babel-jest/build/index.js:325:33)

solution

"Babel - jest" : "^ 27.0.6",- "jest", "^ 26.6.3",
+ "jest" : "^ 27.0.6",
Copy the code

conclusion

Jest support for ESM by default is great, but support is incomplete and Babel is needed. Mocha supports ESM with the following modifications to make it more convenient.

Install esM, then modify test:

"scripts": {
+ "test": "node -r esm ./node_modules/.bin/mocha"
Copy the code

reference

How to resolve “Cannot use import statement outside a module” in jest