Jest and Typescript installation / configuration

Jest

• Cli

yarn global add jest
# or npm
npm install -g jest

• Locally for the project

yarn # if jest is already in package.json
yarn add --dev jest
# or with npm
npm install # if jest is already in package.json
npm install --save-dev jest

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Package.json

Add the npm test script

{
  "scripts": {
    "test": "jest"
  }
}

Configuration file

Generating a conf file

jest --init

module.exports = {
  // All imported modules in your tests should be mocked automatically
  // automock: false,

  // Stop running tests after `n` failures
  // bail: 0,

  // Respect "browser" field in package.json when resolving modules
  // browser: false,

  // The directory where Jest should store its cached dependency information
  // cacheDirectory: "C:\\Users\\gerardnico\\AppData\\Local\\Temp\\jest",

  // Automatically clear mock calls and instances between every test
  // clearMocks: false,

  // Indicates whether the coverage information should be collected while executing the test
  // collectCoverage: false,

  // An array of glob patterns indicating a set of files for which coverage information should be collected
  // collectCoverageFrom: null,

  // The directory where Jest should output its coverage files
  // coverageDirectory: null,

  // An array of regexp pattern strings used to skip coverage collection
  // coveragePathIgnorePatterns: [
  //   "\\\\node_modules\\\\"
  // ],

  // A list of reporter names that Jest uses when writing coverage reports
  // coverageReporters: [
  //   "json",
  //   "text",
  //   "lcov",
  //   "clover"
  // ],

  // An object that configures minimum threshold enforcement for coverage results
  // coverageThreshold: null,

  // A path to a custom dependency extractor
  // dependencyExtractor: null,

  // Make calling deprecated APIs throw helpful error messages
  // errorOnDeprecated: false,

  // Force coverage collection from ignored files using an array of glob patterns
  // forceCoverageMatch: [],

  // A path to a module which exports an async function that is triggered once before all test suites
  // globalSetup: null,

  // A path to a module which exports an async function that is triggered once after all test suites
  // globalTeardown: null,

  // A set of global variables that need to be available in all test environments
  // globals: {},

  // The maximum amount of workers used to run your tests. Can be specified as % or a number. E.g. maxWorkers: 10% will use 10% of your CPU amount + 1 as the maximum worker number. maxWorkers: 2 will use a maximum of 2 workers.
  // maxWorkers: "50%",

  // An array of directory names to be searched recursively up from the requiring module's location
  // moduleDirectories: [
  //   "node_modules"
  // ],

  // An array of file extensions your modules use
  // moduleFileExtensions: [
  //   "js",
  //   "json",
  //   "jsx",
  //   "ts",
  //   "tsx",
  //   "node"
  // ],

  // A map from regular expressions to module names that allow to stub out resources with a single module
  // moduleNameMapper: {},

  // An array of regexp pattern strings, matched against all module paths before considered 'visible' to the module loader
  // modulePathIgnorePatterns: [],

  // Activates notifications for test results
  // notify: false,

  // An enum that specifies notification mode. Requires { notify: true }
  // notifyMode: "failure-change",

  // A preset that is used as a base for Jest's configuration
  // preset: null,

  // Run tests from one or more projects
  // projects: null,

  // Use this configuration option to add custom reporters to Jest
  // reporters: undefined,

  // Automatically reset mock state between every test
  // resetMocks: false,

  // Reset the module registry before running each individual test
  // resetModules: false,

  // A path to a custom resolver
  // resolver: null,

  // Automatically restore mock state between every test
  // restoreMocks: false,

  // The root directory that Jest should scan for tests and modules within
  // rootDir: null,

  // A list of paths to directories that Jest should use to search for files in
  // roots: [
  //   "<rootDir>"
  // ],

  // Allows you to use a custom runner instead of Jest's default test runner
  // runner: "jest-runner",

  // The paths to modules that run some code to configure or set up the testing environment before each test
  // setupFiles: [],

  // A list of paths to modules that run some code to configure or set up the testing framework before each test
  // setupFilesAfterEnv: [],

  // A list of paths to snapshot serializer modules Jest should use for snapshot testing
  // snapshotSerializers: [],

  // The test environment that will be used for testing
  // testEnvironment: "jest-environment-jsdom",

  // Options that will be passed to the testEnvironment
  // testEnvironmentOptions: {},

  // Adds a location field to test results
  // testLocationInResults: false,

  // The glob patterns Jest uses to detect test files
  // testMatch: [
  //   "**/__tests__/**/*.[jt]s?(x)",
  //   "**/?(*.)+(spec|test).[tj]s?(x)"
  // ],

  // An array of regexp pattern strings that are matched against all test paths, matched tests are skipped
  // testPathIgnorePatterns: [
  //   "\\\\node_modules\\\\"
  // ],

  // The regexp pattern or array of patterns that Jest uses to detect test files
  // testRegex: [],

  // This option allows the use of a custom results processor
  // testResultsProcessor: null,

  // This option allows use of a custom test runner
  // testRunner: "jasmine2",

  // This option sets the URL for the jsdom environment. It is reflected in properties such as location.href
  // testURL: "http://localhost",

  // Setting this value to "fake" allows the use of fake timers for functions such as "setTimeout"
  // timers: "real",

  // A map from regular expressions to paths to transformers
  transform: {}, // babel-jest is automatically installed when installing Jest and will automatically transform files

  // An array of regexp pattern strings that are matched against all source file paths, matched files will skip transformation
  // transformIgnorePatterns: [
  //   "\\\\node_modules\\\\"
  // ],

  // An array of regexp pattern strings that are matched against all modules before the module loader will automatically return a mock for them
  // unmockedModulePathPatterns: undefined,

  // Indicates whether each individual test should be reported during the run
  // verbose: null,

  // An array of regexp patterns that are matched against all source file paths before re-running tests in watch mode
  // watchPathIgnorePatterns: [],

  // Whether to use watchman for file crawling
  // watchman: true,
};

Babel

Babel is needed with Jest:

• to understand ES6 modules (no import statement in Node). Babel will be used to transpiler the import statement of Es6.
• to supports TypeScript

Installation:

• Babel

yarn add --dev babel-jest @babel/core babel-cli
# or
npm install --save-dev babel-jest babel-core babel-cli

• Preset (babel-preset-env and typescript)

yarn add --dev @babel/preset-env #es module
yarn add --dev @babel/preset-typescript # typescript
# or
npm install --save-dev babel/preset-env
npm install --save-dev @babel/preset-typescript #typescript

• To enable the preset

module.exports = api => {
    const isTest = api.env('test');
    // You can use isTest to determine what presets and plugins to use.

    return {
        presets: [
            [
                '@babel/preset-env',
                '@babel/preset-typescript',
                {
                    targets: {
                        node: 'current',
                    },
                },
            ],
        ],
    };

};

SyntaxError: Cannot use import statement outside a module

> jest

 FAIL  __tests__/country.test.ts
  ● Test suite failed to run

    D:\dokuwiki\lib\plugins\webcomponent\__tests__\country.test.ts:1
    ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,global,jest){import * as Country from "../js/Country";
                                                                                             ^^^^^^

    SyntaxError: Cannot use import statement outside a module

      at ScriptTransformer._transformAndBuildScript (node_modules/@jest/transform/build/ScriptTransformer.js:537:17)
      at ScriptTransformer.transform (node_modules/@jest/transform/build/ScriptTransformer.js:579:25)

If you are using typescript, add ts-jest