Test an .js.erb file with Rails + Webpacker + Jest

Question

I have a Rails 5 app which uses webpacker, with a file app/javascript/packs/components/module_one.js which I'm trying to test with Jest. This file contains an import to an .js.erb file as follows:

// app/javascript/packs/components/module_one.js

import ModuleTwo from './module_two.js.erb'

// ...

module_two.js.erb contains the following:

// app/javascript/packs/components/module_two.js.erb

import ModuleOne from './module_one'

// ...

While running webpack-dev-server everything works as expected, but when I try to run yarn test, it complains with the following error:

FAIL  app/javascript/test/module_one.test.js
  ● Test suite failed to run

    /path/to/module_two.js.erb:1
    ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,global,jest){import ModuleOne from './module_one'
                                                                                             ^^^^^^
    SyntaxError: Unexpected token import

      at ScriptTransformer._transformAndBuildScript (node_modules/jest-runtime/build/script_transformer.js:306:17)
      at Object.<anonymous> (app/javascript/packs/components/module_one.js:1:745)
      at Object.<anonymous> (app/javascript/test/module_one.test.js:1:124)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        2.545s
Ran all test suites.
error Command failed with exit code 1.

So it seems like the module_two.js.erb file is not being transformed properly from ES6, because when I remove the first line of module_one.js, it doesn't complain anymore.

Here is my current setup:

// .babelrc

{
  "presets": [
    ["env", {
      "modules": false,
      "targets": {
        "browsers": "> 1%",
        "uglify": true
      },
      "useBuiltIns": true
    }]
  ],

  "plugins": [
    "syntax-dynamic-import",
    ["transform-class-properties", { "spec": true }]
  ],

  "env": {
    "test": {
      "plugins": ["transform-es2015-modules-commonjs"]
    }
  }
}

---

// package.json

{
  // ...
  "devDependencies": {
    "babel-jest": "^21.0.2",
    "jest": "^21.0.2",
    "regenerator-runtime": "^0.11.0",
    "webpack-dev-server": "^2.7.1"
  },
  "scripts": {
    "test": "jest"
  },
  "jest": {
    "roots": [
      "<rootDir>/app/javascript/test"
    ],
    "moduleDirectories": [
      "<rootDir>/node_modules"
    ],
    "moduleFileExtensions": [
      "js",
      "jsx",
      "erb"
    ],
    "transform": {
      "^.+\\.jsx?$": "babel-jest",
      "ˆ.+\\.jsx?.erb": "rails-erb-loader"
    }
  }
}

Answer 1

In case someone else bumps into this. Your .babelrc seems to be missing "es2015" preset. Here is well explained about this and other issues configuring JS testing with Rails + Webpacker.