Explore Jest Config and Lifecycle

Simple Setup

• Checkout simple_setup branch
• yarn install

Run:

yarn tl

You should see some logs show up and this should give you some idea of the lifecycle.

🎉🎉 Congrats! You have a working setup!

Explore Global Variables

(global Documentation)

Set of global variables → made available in all test environments

• Checkout explore_globals branch
• See jest.config.js

module.exports = {
    globals: {
        __NODE_DEBUG__: process.env.NODE_DEBUG,
    },
};

• Accessing __NODE_DEBUG__ value

console.log(`Current __NODE_DEBUG__ value is ${global.__NODE_DEBUG__}`);

Try running:

• yarn tl
• yarn tlb (this runs the tests one after another and uses --runInBand)

Result:

• Any mutation won't reflect between tests (even in the same test runs) although the mutation will be reflected for that particular test file
  • so any changes in it block is seen in afterEach block
• Values for global variables must be json-serializable.
  • You can't create a function and try using this function in your test!
  • Use setupFiles config instead

Explore Global Setup and Global Teardown

(globalSetup Documentation) (globalTeardown Documentation)

• Checkout global_setup_teardown branch
• See jest.config.js

    globalSetup: './configFiles/globalSetup.js',
    globalTeardown: './configFiles/globalTeardown.js',

Try running:

• yarn tl
• yarn tlb

Results:

• Any global variable defined in globalSetup can be read in globalTeardown but it cannot be read by any of the tests or test-suite
• global variable defined in jest.config.js cannot be read in globalSetup and globalTeardown
• Execution Sequence: globalSetup → ...[beforeAll, beforeEach, test, afterEach, afterAll]... → globalTeardown
• globalConfig passed to globalSetup and globalTeardown functions cannot bo modified!

Explore SetupFiles and SetupFilesAfterEnv

(setupFiles Documentation) (setupFilesAfterEnv Documentation)

• Checkout setupfiles branch
• See jest.config.js

    setupFiles: ['./configFiles/setupFile1.js', './configFiles/setupFile2.js'],
    setupFilesAfterEnv: [
        './configFiles/setupFileAfterEnv1.js',
        './configFiles/setupFileAfterEnv2.js',
    ],

Try running:

• yarn tlb (--runInBand to see the behavior)

Result:

• setupFiles and setupFileAfterEnv can access variables declared using global
• setupFiles can be used to create and set functions on global and these can be accessed in setupFilesAfterEnv as well as in your Test files (ex: funnyHelloWorld function created by setupFile1.js)
• setupFiles and setupFileAfterEnv are executed before each test file
• setupFiles is expected to be used to run some code to setup your environment before every test is run
  • you don't have access to functions like beforeAll, beforeEach, afterAll, afterEach
• setupFilesAfterEnv is expected to be used to configure the testing framework before each test file but after the the testing framework is installed in the environment. Think of it as the right place to run some common code that needs to happen for every test to customize the testing framework for your needs.
  • you have access to functions like beforeAll, beforeEach, afterAll, afterEach
• Lifecycle looks like:
  • globalSetup
  • For each test file
    • setupFile
    • setupFileAfterEnv
    • beforeAll from setupFileAfterEnv
    • beforeAll from test file
    • beforeEach from setupFileAfterEnv
    • beforeEach from test file
    • set of test from the file
    • afterEach from test file
    • afterEach from setupFileAfterEnv
    • afterAll from test file
    • afterAll from setupFileAfterEnv
  • globalTeardown

Explore Test Environment

(testEnvironment Documentation) (testEnvironmentOptions Documentation)

• Checkout explore_globals branch
• run yarn install
• See jest.config.js

    testEnvironment: './configFiles/customTestEnvironment.js',
    testEnvironmentOptions: {
        teKey1: 'teValue1',
        teKey2: 'teValue2',
    },
    testRunner: 'jest-circus/runner', // we are including this as well!

Try running:

• yarn tl

Result:

• Lifecycle looks like:
  • globalSetup
  • For each test file
    • customTestEnvironment is instantiated: constructor
    • setupFile
    • customTestEnvironment setup
    • setupFileAfterEnv
    • beforeAll from setupFileAfterEnv
    • beforeAll from test file
    • customTestEnvironment handleTestEvent - test_start
    • beforeEach from setupFileAfterEnv
    • beforeEach from test file
    • customTestEnvironment handleTestEvent - test_fn_start
    • set of tests from the file
    • afterEach from test file
    • afterEach from setupFileAfterEnv
    • afterAll from test file
    • afterAll from setupFileAfterEnv
    • customTestEnvironment teardown
  • globalTeardown
• runScripts is not used if getVmContext is defined in customTestEnvironment
• handleTestEvent is used by jest-circus/runner and if it is not set as your runner, this function is never called
• setup can be used to set up more variables or functions on global (example, we set up __NEW_VALUE__ in our code) and they will be available in tests for consumption
• values passed using testEnvironmentOptions in jest.config.js can be accessed in customTestEnvironment and in our tests as well

Explore Runner

(runner Documentation)

• Checkout runner branch
• See jest.config.js

    runner: './configFiles/customRunner.js',

Try running:

• yarn tl

Results:

• you can create your own custom Runner (default is jest-runner in previous example we used jest-circus)
• Lifecycle looks like:
  • globalSetup
  • customRunner gets initialized
  • customRunner's runTests is called with with list of tests (responsible for running these tests)
  • For each test file (based on logic inside runTests these test files can run in parallel or sequentially)
    • customTestEnvironment is instantiated: constructor
    • setupFile
    • customTestEnvironment setup
    • setupFileAfterEnv
    • beforeAll from setupFileAfterEnv
    • beforeAll from test file
    • customTestEnvironment handleTestEvent - test_start
    • beforeEach from setupFileAfterEnv
    • beforeEach from test file
    • customTestEnvironment handleTestEvent - test_fn_start
    • set of tests from the file
    • afterEach from test file
    • afterEach from setupFileAfterEnv
    • afterAll from test file
    • afterAll from setupFileAfterEnv
    • customTestEnvironment teardown
  • globalTeardown
• We rely on default jest-runner's runTest function in the code (I am sure we can build our own as well!)
  • this internally calls jest-jasmine or jest-circus/runner (when process.env.JEST_CIRCUS === '1')
• We can also customize the execution a little bit by modifying the value returned by runTest

We forced CLI to display ✕ even though the test passed by modifying the value to failed

Explore Test Runner

(testRunner Documentation)

• Checkout testRunner branch
• See jest.config.js

    testRunner: './configFiles/customTestRunner.js',

Try running:

• yarn tl

Results:

• You can create your own custom Test Runner (default is jest-jasmine2 or we can even use jest-circus/runner)
• Lifecycle looks like:
  • globalSetup
  • customRunner gets initialized
  • customRunner's runTests is called with with list of tests (responsible for running these tests)
  • For each test file (based on logic inside runTests these test files can run in parallel or sequentially)
    • customTestEnvironment is instantiated: constructor
    • setupFiles
    • customTestEnvironment -> setup()
    • customTestRunner is invoked
      • setupFileAfterEnv
      • beforeAll from setupFileAfterEnv
      • beforeAll from test file
      • customTestEnvironment handleTestEvent - test_start (only with jest-circus)
      • beforeEach from setupFileAfterEnv
      • beforeEach from test file
      • customTestEnvironment handleTestEvent - test_fn_start (only with jest-circus)
      • set of tests from the file
      • afterEach from test file
      • afterEach from setupFileAfterEnv
      • afterAll from test file
      • afterAll from setupFileAfterEnv
    • customTestEnvironment teardown
  • globalTeardown
• This is responsible for running the actual test and knows what to do when we encounter test functions like beforeAll, beforeEach, afterAll, afterEach, 'it or describe

In the code example, the customTestRunner randomly picks one of jest-jasmine2 or jest-circus/runner and runs the tests through them.