Importing images breaks jest test

Question

In React components importing assets (ex, import logo from "../../../assets/img/logo.png) gives such error

({"Object.":function(module,exports,require,__dirname,__filename,global,jest){�PNG
SyntaxError: Invalid or unexpected token at ScriptTransformer._transformAndBuildScript (node_modules/jest-runtime/build/script_transformer.js:305:17)

my jest config is

"jest": {
"testRegex": ".*\\.spec\\.js$",
"moduleFileExtensions": [
  "js",
  "jsx",
  "json"
],
"moduleDirectories": [
  "node_modules",
  "src",
  "assets"
],
"moduleNameMapper": {
  "\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$/": "<rootDir>/__mocks__/fileMock.js",
  "\\.(css|less|scss)$": "<rootDir>/__mocks__/styleMock.js"
},
"verbose": true,
"bail": true
}

what am i missing?

Answer 1

When you import image files, Jest tries to interpret the binary codes of the images as .js, hence runs into errors.

The only way out is to mock a default response anytime jest sees an image import!

How do we do this?

• first you tell Jest to run the mock file each time an image import is encountered. you do this by adding the key below to your package.json file

"jest": {
 "moduleNameMapper": {
      "\\.(jpg|ico|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$": "<rootDir>/__mocks__/fileMock.js",
      "\\.(css|less)$": "<rootDir>/__mocks__/fileMock.js"
    }
}

Note: if you already have the "Jest" key, just add the "moduleNameMapper" child in it

• lastly, create a mocks folder in your root and create fileMock.js file inside it. populate the file with the snippet below

module.exports = ''; 

Note: If you are using es6 you can use export default ''; to avoid an Eslint flag

when you are done with the above steps, you can restart the test and you are good to go.

Note. remember to add the varying extensions of your image files in the moduleNameMapper so that they can be mocked.

I hope I have been able to help. #cheers!

Answer 2

For anyone looking into this problem. You have to do install npm install --save-dev identity-obj-proxy to get the necessary dependencies.

"jest": {
    "moduleNameMapper": {
      ".+\\.(css|styl|less|sass|scss|png|jpg|ttf|woff|woff2)$": "identity-obj-proxy"
    }
  }

Answer 3

If you want to use jest with webpack, you need to explicitly configure it as so. Take a look at this guide here: http://facebook.github.io/jest/docs/en/webpack.html

Answer 4

I had the same problem and I solved it as follows:

1. npm install -D jest-transform-stub
2. Then, in package.json, I added the following transformation:

    "jest": {
        ...
        "transform": {
            ...
            ".+\\.(css|scss|png|jpg|svg)$": "jest-transform-stub"

Answer 5

In case of IOS image names with @

moduleNameMapper: {
    "^image![a-zA-Z0-9$_-]+$": "GlobalImageStub",
    "^[@./a-zA-Z0-9$_-]+\\.(png|gif)$": "RelativeImageStub"
  }

Answer 6

I had this same issue! I'm not sure if it's the same case as in the original question, but for me jest was still somehow trying to load the images as JS and trying to parse them while I had the files matching image extensions mapped to a mock in moduleNameMapper. My file also included some code to map the @ character to the root src directory, since I had webpack and this was configured as a webpack alias in the project (and in TS). The full moduleNameMapper entry in jest.config.js looked like this for me:

    moduleNameMapper: {
        '^@$': '<rootDir>/src',
        '^@/(.*)':
            '<rootDir>/src/$1',
        '\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$':
            '<rootDir>/__mocks__/fileMock.js',
        // '\\.(css|less)$': '<rootDir>/__mocks__/styleMock.js',
        '.*\\.(css|less)$': 'identity-obj-proxy',
    }

For me it turned out that when I was importing the images in my components, the path was something like: '@/assets/someImage.jpg'. However, it seems this would match the first regex first, the one covering the @ alias: ^@/(.*). Thus, it was being mapped to <rootDir>/src/$1 instead of the <rootDir>/__mocks__/fileMock.js.

I fixed it by making the alias only match non-images:

    moduleNameMapper: {
        '^@$': '<rootDir>/src',
        '^@/(.*)\\.(?!jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$':
            '<rootDir>/src/$1',
        '.*\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$':
            '<rootDir>/__mocks__/fileMock.js',
        // '\\.(css|less)$': '<rootDir>/__mocks__/styleMock.js',
        '.*\\.(css|less)$': 'identity-obj-proxy',
    }