How can I stop my React Native tests bombing out on Flow types in Node Modules?

Question

I am trying to set up testing on an existing React Native project. When I run a test with Jest, the test bombs out with the following error:

Test suite failed to run

   ...etc/__app__/node_modules/react-native/Libraries/polyfills/error-guard.js:14
    type ErrorHandler = (error: mixed, isFatal: boolean) => void;
         ^^^^^^^^^^^^

    SyntaxError: Unexpected identifier
      at ScriptTransformer._transformAndBuildScript (node_modules/@jest/transform/build/ScriptTransformer.js:537:17)
      at ScriptTransformer.transform (node_modules/@jest/transform/build/ScriptTransformer.js:579:25)
      at Object.<anonymous> (node_modules/react-native/jest/setup.js:16:6)

The unexpected identifier is the following:

 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @format
 * @flow strict
 * @polyfill
 */

let _inGuard = 0;

type ErrorHandler = (error: mixed, isFatal: boolean) => void;

I surmised the issue is related to the separation of the React and Flow presets.

The code in node_modules, has Flowtype syntax in it. My Babel configuration applies to my own code, but not to files in node_modules.

My babel.config.js:

  presets: ['module:metro-react-native-babel-preset', "@babel/preset-flow", "@babel/plugin-transform-flow-strip-types"],
};

My Jest package.json:

"jest": {
    "verbose": true,
    "preset": "react-native",
    "transformIgnorePatterns": [
      "node_modules/(?!react-native|@tableflip/react-native-navbar)",
      "/node_modules/(?!@babel/runtime)",
      "node_modules/(?!(react-native|__app__|react-native-button)/)",
      "/node_modules/(?!react-native)/.+"

    ],
    "setupFilesAfterEnv": [
      "<rootDir>/node_modules/riteway-jest/src/riteway-jest.js"
    ]
  },

How can I stop my tests bombing out on Flow types in Node Modules?

EDIT: Full package.JSON

{
  "name": "ReactNativeTest",

  "scripts": {
    "start": "node node_modules/react-native/local-cli/cli.js start",
    "start:ios": "react-native run-ios && react-native log-ios",
    "start:android": "react-native run-android && react-native log-android",
    "start:ios:debug": "react-native run-ios --simulator=\"iPhone X\" & open \"rndebugger://set-debugger-loc?host=localhost&port=8081\"",
    "start:android:debug": "react-native run-android & open \"rndebugger://set-debugger-loc?host=localhost&port=8081\"",
    "start:debug": "open \"rndebugger://set-debugger-loc?host=localhost&port=8081\"",
    "lint": "standard",
    "test": "jest"
  },
  "dependencies": {
    "@babel/preset-env": "^7.8.4",
    "@babel/runtime": "7.0.0-beta.55",
    "@expo/react-native-action-sheet": "3.4.0",
    "@react-native-community/async-storage": "1.6.3",
    "@react-native-community/netinfo": "4.6.1",
    "@react-native-community/viewpager": "3.3.0",
    "babel-core": "^7.0.0-bridge.0",
    "babel-preset-react-app": "^7.0.0",
    "ejson": "2.2.0",
    "lodash-es": "4.17.15",
    "lodash.isstring": "4.0.1",
    "markdown-it": "10.0.0",
    "meteor-standalone-random": "1.0.67",
    "moment": "2.24.0",
    "prop-types": "15.7.2",
    "react": "16.12.0",
    "react-native": "0.61.5",
    "react-native-calendar-events": "1.7.3",
    "react-native-config": "0.11.7",
    "react-native-dismiss-keyboard": "1.0.0",
    "react-native-firebase": "5.6.0",
    "react-native-hyperlink": "0.0.16",
    "react-native-image-picker": "1.1.0",
    "react-native-iphone-x-helper": "1.2.1",
    "react-native-joi": "0.0.5",
    "react-native-keyboard-aware-scroll-view": "0.9.1",
    "react-native-keyboard-spacer": "0.4.1",
    "react-native-maps": "0.26.1",
    "react-native-onesignal": "3.5.0",
    "react-native-scrollable-tab-view": "1.0.0",
    "react-native-select-multiple": "2.1.0",
    "react-native-side-menu": "1.1.3",
    "react-native-swiper": "1.5.14",
    "react-native-thumbnail-video": "0.1.2",
    "react-native-touch-id": "4.4.1",
    "react-native-uploadcare-image": "2.0.0",
    "react-native-video": "5.0.2",
    "react-native-webview": "7.5.2",
    "react-redux": "7.1.3",
    "reduce-reducers": "1.0.4",
    "redux": "4.0.4",
    "redux-devtools-extension": "2.13.8",
    "redux-localstorage": "github:tableflip/redux-localstorage#fix-buffer-main-src",
    "redux-localstorage-filter": "0.1.1",
    "redux-thunk": "2.3.0",
    "url": "0.11.0",
    "uuid": "3.3.3"
  },
  "jest": {
    "verbose": true,
    "preset": "react-native",
    "transformIgnorePatterns": [
      "<rootDir>/node_modules/(?!@babel/runtime)",
      "<rootDir>node_modules/(?!(react-native|__app__|react-native-button)/)",
      "/node_modules/(?!react-native)/.+",
      "/node_modules/"
    ],
    "setupFilesAfterEnv": [
      "<rootDir>/src/riteway-jest.js"
    ]
  },
  "devDependencies": {
    "@babel/core": "^7.7.4",
    "@babel/plugin-transform-flow-strip-types": "^7.8.3",
    "@babel/plugin-transform-runtime": "^7.8.3",
    "@babel/preset-flow": "^7.8.3",
    "babel-eslint": "10.0.3",
    "babel-jest": "^24.9.0",
    "babel-plugin-import-rename": "1.0.1",
    "jest": "24.9.0",
    "jetifier": "1.6.4",
    "metro-react-native-babel-preset": "0.57.0",
    "react-native-config-node": "0.0.2",
    "react-test-renderer": "16.12.0",
    "redux-mock-store": "1.5.3",
    "riteway-jest": "^2.0.2",
    "standard": "14.3.1"
  },
  "standard": {
    "parser": "babel-eslint",
    "globals": [
      "fetch",
      "FormData",
      "it",
      "expect"
    ]
  },
  "transform": {
    "^.+\\.[t|j]sx?$": "babel-jest"
  }
}

Answer 1

In my case, I needed to add @react-native with '@' into transformIgnorePatterns as shown bellow:

"transformIgnorePatterns": [
  "node_modules/(?!(@react-native|react-native)/)"
]

Answer 2

First, we need to understand what is the root cause.

SyntaxError: Unexpected identifier

Basically, these types of errors occurred due to your jest configuration. If you are instructed to transform all the libraries inside the node_modules it will raise these types of erros. So please go ahead and check for the below statement in your package.json jest configuration.

transformIgnorePatterns

Above is using to add some transformation ignore patterns and it will have the this default regex pattern => ["/node_modules/", "\\.pnp\\.[^\\\/]+$"]

Below is from the official jest documentation:

Sometimes it happens (especially in React Native or TypeScript projects) that 3rd party modules are published as untranspiled. Since all files inside node_modules are not transformed by default, Jest will not understand the code in these modules, resulting in syntax errors. To overcome this, you may use transformIgnorePatterns to allow transpiling such modules. You'll find a good example of this use case in React Native Guide.

So try adding below as instructed by @Pavot in one of the answers will help fix. But if it's a similar issue that occurred by a different library, you can try adding it to the transform ignore list and see whether it works or not.

"transformIgnorePatterns": [
  "node_modules/(?!(@react-native|react-native)/)"
]

Answer 3

There is issue with transformIgnorePatterns in package.json. Instead of adding number of items in this, just follow this pattern to add modules to blacklist.

"transformIgnorePatterns": [
      "node_modules/(?!MODULE_NAME_1|MODULE_NAME_2)/"
    ], 

As from your error, we need to add react-native to transformIgnorePatterns. Actually, we need to add all those modules in blacklist that throws error because mostly modules are not written completely in JS.

Finally in my case the jest in package.json is

"jest": {
    "preset": "react-native",
    "transformIgnorePatterns": [
      "node_modules/(?!react-native-payfort-sdk|react-native)/"
    ],
    "globals": {
      "__DEV__": true
    },
    "testEnvironment": "node"
  }

This worked for me and hopefully this will help you as well.

Answer 4

Babel might need an according preset. If you are outside Expo, npm install --save-dev metro-react-native-babel-preset and insert this to your babel.config.js:

module.exports = {
  presets: ['module:metro-react-native-babel-preset'],
};