前端自动化测试框架 Jest 极简教程

Delightful JavaScript Testing. https://jestjs.io

Jest是由Facebook发布的开源的、基于Jasmine的JavaScript单元测试框架。集成了 Mocha，chai，jsdom，sinon等功能。

具有零配置、内置代码覆盖率、强大的Mocks等特点。

Jest源于测试Web聊天应用。Facebook的一名软件工程师Jeff Morrison半年前又重拾这个项目，改善它的性能，并将其开源。

Jest的目标是减少开始测试一个项目所要花费的时间和认知负荷，因此它提供了大部分你需要的现成工具：快速的命令行接口、Mock工具集以及它的自动模块Mock系统。此外，如果你在寻找隔离工具例如Mock库，大部分其它工具将让你在测试中（甚至经常在你的主代码中）写一些不尽如人意的样板代码，以使其生效。

Jest与Jasmine框架的区别是在后者之上增加了一些层。最值得注意的是，运行测试时，Jest会自动模拟依赖。Jest自动为每个依赖的模块生成Mock，并默认提供这些Mock，这样就可以很容易地隔离模块的依赖。

Jest 测试的生命周期

jest 测试提供了一些测试的生命周期 API，可以辅助我们在每个 case 的开始和结束做一些处理。 这样，在进行一些和数据相关的测试时，可以在测试前准备一些数据，在测试后，清理测试数据。

4 个主要的生命周期函数：

• beforeAll(fn, timeout): 同 afterAll，不同之处在于在所有测试开始前执行

• beforeEach(fn, timeout): 同 afterEach，不同之处在于在每个测试开始前执行

• afterEach(fn, timeout): 每个 test 执行完后执行 fn，timeout 含义同上

• afterAll(fn, timeout): 当前文件中的所有测试执行完成后执行 fn, 如果 fn 是 promise，jest 会等待 timeout 毫秒，默认 5000.

配置项

1. testMatch
   设置识别哪些文件是测试文件（glob形式），与testRegex互斥，不能同时写

testMatch: ['\*\*/\_\_tests\_\_/\*\*/\*.js?(x)','\*\*/?(*.)(spec|test).js?(x)']

2. testRegex
   设置识别哪些文件是测试文件（正则形式），与testMatch互斥，不能同时写

testRegex: '(/\_\_tests\_\_).*|(\\\\.|/)(test|spec))\\\\.jsx?$'

3. testRnviroment
   测试环境，默认值是：jsdom，可修改为node

testEnvironment: 'jsdom'

4. rootDir
   默认值：当前目录，一般是package.json所在的目录。

rootDir: ' '

5. moduleFileExtensions
   测试文件的类型

moduleFileExtensions: ['js','json','jsx','node']

一般配置：

module.exports = {
    testMatch: ['<rootDir>/test/\*\*/\*.js'],
    testEnvironment: 'jsdom',
    rootDir: '',
    moduleFileExtensions: ['js','json','jsx','node']
}

Jest CLI Options

id: cli
title: Jest CLI Options

The jest command line runner has a number of useful options. You can run jest --help to view all available options. Many of the options shown below can also be used together to run tests exactly the way you want. Every one of Jest's Configuration options can also be specified through the CLI.

Here is a brief overview:

Running from the command line

Run all tests (default):

jest

Run only the tests that were specified with a pattern or filename:

jest my-test #or
jest path/to/my-test.js

Run tests related to changed files based on hg/git (uncommitted files):

jest -o

Run tests related to path/to/fileA.js and path/to/fileB.js:

jest --findRelatedTests path/to/fileA.js path/to/fileB.js

Run tests that match this spec name (match against the name in describe or test, basically).

jest -t name-of-spec

Run watch mode:

jest --watch #runs jest -o by default
jest --watchAll #runs all tests

Watch mode also enables to specify the name or path to a file to focus on a specific set of tests.

Using with yarn

If you run Jest via yarn test, you can pass the command line arguments directly as Jest arguments.

Instead of:

jest -u -t="ColorPicker"

you can use:

yarn test -u -t="ColorPicker"

Using with npm scripts

If you run Jest via npm test, you can still use the command line arguments by inserting a -- between npm test and the Jest arguments.

Instead of:

jest -u -t="ColorPicker"

you can use:

npm test -- -u -t="ColorPicker"

Camelcase & dashed args support

Jest supports both camelcase and dashed arg formats. The following examples will have equal result:

jest --collect-coverage
jest --collectCoverage

Arguments can also be mixed:

jest --update-snapshot --detectOpenHandles

Options

Note: CLI options take precedence over values from the Configuration.

Reference

jest <regexForTestFiles>

When you run jest with an argument, that argument is treated as a regular expression to match against files in your project. It is possible to run test suites by providing a pattern. Only the files that the pattern matches will be picked up and executed. Depending on your terminal, you may need to quote this argument: jest "my.*(complex)?pattern". On Windows, you will need to use / as a path separator or escape \ as \\.

--bail

Alias: -b. Exit the test suite immediately upon n number of failing test suite. Defaults to 1.

--cache

Whether to use the cache. Defaults to true. Disable the cache using --no-cache. Note: the cache should only be disabled if you are experiencing caching related problems. On average, disabling the cache makes Jest at least two times slower.

If you want to inspect the cache, use --showConfig and look at the cacheDirectory value. If you need to clear the cache, use --clearCache.

--changedFilesWithAncestor

Runs tests related to the current changes and the changes made in the last commit. Behaves similarly to --onlyChanged.

--changedSince

Runs tests related the changes since the provided branch. If the current branch has diverged from the given branch, then only changes made locally will be tested. Behaves similarly to --onlyChanged.

--ci

When this option is provided, Jest will assume it is running in a CI environment. This changes the behavior when a new snapshot is encountered. Instead of the regular behavior of storing a new snapshot automatically, it will fail the test and require Jest to be run with --updateSnapshot.

--clearCache

Deletes the Jest cache directory and then exits without running tests. Will delete cacheDirectory if the option is passed, or Jest's default cache directory. The default cache directory can be found by calling jest --showConfig. Note: clearing the cache will reduce performance.

--collectCoverageFrom=<glob>

A glob pattern relative to <rootDir> matching the files that coverage info needs to be collected from.

--colors

Forces test results output highlighting even if stdout is not a TTY.

--config=<path>

Alias: -c. The path to a Jest config file specifying how to find and execute tests. If no rootDir is set in the config, the directory containing the config file is assumed to be the rootDir for the project. This can also be a JSON-encoded value which Jest will use as configuration.

--coverage

Indicates that test coverage information should be collected and reported in the output. This option is also aliased by --collectCoverage.

--debug

Print debugging info about your Jest config.

--detectOpenHandles

Attempt to collect and print open handles preventing Jest from exiting cleanly. Use this in cases where you need to use --forceExit in order for Jest to exit to potentially track down the reason. Implemented using async_hooks, so it only works in Node 8 and newer.

--env=<environment>

The test environment used for all tests. This can point to any file or node module. Examples: jsdom, node or path/to/my-environment.js.

--errorOnDeprecated

Make calling deprecated APIs throw helpful error messages. Useful for easing the upgrade process.

--expand

Alias: -e. Use this flag to show full diffs and errors instead of a patch.

--findRelatedTests <spaceSeparatedListOfSourceFiles>

Find and run the tests that cover a space separated list of source files that were passed in as arguments. Useful for pre-commit hook integration to run the minimal amount of tests necessary. Can be used together with --coverage to include a test coverage for the source files, no duplicate --collectCoverageFrom arguments needed.

--forceExit

Force Jest to exit after all tests have completed running. This is useful when resources set up by test code cannot be adequately cleaned up. Note: This feature is an escape-hatch. If Jest doesn't exit at the end of a test run, it means external resources are still being held on to or timers are still pending in your code. It is advised to tear down external resources after each test to make sure Jest can shut down cleanly. You can use --detectOpenHandles to help track it down.

--help

Show the help information, similar to this page.

--init

Generate a basic configuration file. Based on your project, Jest will ask you a few questions that will help to generate a jest.config.js file with a short description for each option.

--json

Prints the test results in JSON. This mode will send all other test output and user messages to stderr.

--outputFile=<filename>

Write test results to a file when the --json option is also specified.

--lastCommit

Run all tests affected by file changes in the last commit made. Behaves similarly to --onlyChanged.

--listTests

Lists all tests as JSON that Jest will run given the arguments, and exits. This can be used together with --findRelatedTests to know which tests Jest will run.

--logHeapUsage

Logs the heap usage after every test. Useful to debug memory leaks. Use together with --runInBand and --expose-gc in node.

--maxWorkers=<num>|<string>

Alias: -w. Specifies the maximum number of workers the worker-pool will spawn for running tests. This defaults to the number of the cores available on your machine. It may be useful to adjust this in resource limited environments like CIs but the default should be adequate for most use-cases.

For environments with variable CPUs available, you can use percentage based configuration: --maxWorkers=50%

--noStackTrace

Disables stack trace in test results output.

--notify

Activates notifications for test results. Good for when you don't want your consciousness to be able to focus on anything except JavaScript testing.

--onlyChanged

Alias: -o. Attempts to identify which tests to run based on which files have changed in the current repository. Only works if you're running tests in a git/hg repository at the moment and requires a static dependency graph (ie. no dynamic requires).

--passWithNoTests

Allows the test suite to pass when no files are found.

--projects <path1> ... <pathN>

Run tests from one or more projects, found in the specified paths; also takes path globs. This option is the CLI equivalent of the projects configuration option. Note that if configuration files are found in the specified paths, all projects specified within those configuration files will be run.

--reporters

Run tests with specified reporters. Reporter options are not available via CLI. Example with multiple reporters:

jest --reporters="default" --reporters="jest-junit"

--runInBand

Alias: -i. Run all tests serially in the current process, rather than creating a worker pool of child processes that run tests. This can be useful for debugging.

--runTestsByPath

Run only the tests that were specified with their exact paths.

Note: The default regex matching works fine on small runs, but becomes slow if provided with multiple patterns and/or against a lot of tests. This option replaces the regex matching logic and by that optimizes the time it takes Jest to filter specific test files

--setupTestFrameworkScriptFile=<file>

The path to a module that runs some code to configure or set up the testing framework before each test. Beware that files imported by the setup script will not be mocked during testing.

--showConfig

Print your Jest config and then exits.

--silent

Prevent tests from printing messages through the console.

--testNamePattern=<regex>

Alias: -t. Run only tests with a name that matches the regex. For example, suppose you want to run only tests related to authorization which will have names like "GET /api/posts with auth", then you can use jest -t=auth.

Note: The regex is matched against the full name, which is a combination of the test name and all its surrounding describe blocks.

--testLocationInResults

Adds a location field to test results. Useful if you want to report the location of a test in a reporter.

Note that column is 0-indexed while line is not.

{
  "column": 4,
  "line": 5
}

--testPathPattern=<regex>

A regexp pattern string that is matched against all tests paths before executing the test. On Windows, you will need to use / as a path separator or escape \ as \\.

--testPathIgnorePatterns=[array]

An array of regexp pattern strings that is tested against all tests paths before executing the test. Contrary to --testPathPattern, it will only run those test with a path that does not match with the provided regexp expressions.

--testRunner=<path>

Lets you specify a custom test runner.

--updateSnapshot

Alias: -u. Use this flag to re-record every snapshot that fails during this test run. Can be used together with a test suite pattern or with --testNamePattern to re-record snapshots.

--useStderr

Divert all output to stderr.

--verbose

Display individual test results with the test suite hierarchy.

--version

Alias: -v. Print the version and exit.

--watch

Watch files for changes and rerun tests related to changed files. If you want to re-run all tests when a file has changed, use the --watchAll option instead.

--watchAll

Watch files for changes and rerun all tests when something changes. If you want to re-run only the tests that depend on the changed files, use the --watch option.

--watchman

Whether to use watchman for file crawling. Defaults to true. Disable using --no-watchman.