Jest

Painless JavaScript Unit Testing

• Familiar Approach: Built on top of the Jasmine test framework, using familiar expect(value).toBe(other) assertions

• Mock by Default: Automatically mocks CommonJS modules returned by require(), making most existing code testable

• Short Feedback Loop: DOM APIs are mocked and tests run in parallel via a small node.js command line utility

Getting Started

Check out the Getting Started tutorial. It's pretty simple!

API

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The jest object

• jest.addMatchers(matchers)
• jest.autoMockOff()
• jest.autoMockOn()
• jest.clearAllTimers()
• jest.currentTestPath()
• jest.fn(implementation?)
• jest.genMockFromModule(moduleName)
• jest.mock(moduleName)
• jest.runAllTicks()
• jest.runAllTimers()
• jest.runOnlyPendingTimers()
• jest.setMock(moduleName, moduleExports)
• jest.unmock(moduleName)

Mock functions

Mock functions can be created using jest.fn().

• mockFn.mock.calls
• mockFn.mock.instances
• mockFn.mockClear()
• mockFn.mockImplementation(fn)
• mockFn.mockReturnThis()
• mockFn.mockReturnValue(value)
• mockFn.mockReturnValueOnce(value)

require extensions

• require.requireActual(moduleName)
• require.requireMock(moduleName)

Config options

• config.automock [boolean]
• config.bail [boolean]
• config.cache [boolean]
• config.cacheDirectory [string]
• config.collectCoverage [boolean]
• config.collectCoverageOnlyFrom [object]
• config.globals [object]
• config.mocksPattern [string]
• config.moduleFileExtensions [array]
• config.modulePathIgnorePatterns [array]
• config.moduleNameMapper [object<string, string>]
• config.preprocessCachingDisabled [boolean]
• config.rootDir [string]
• config.scriptPreprocessor [string]
• config.preprocessorIgnorePatterns [array]
• config.setupFiles [array]
• config.setupTestFrameworkScriptFile [string]
• config.testDirectoryName [string]
• config.testFileExtensions [array]
• config.testPathDirs [array]
• config.testPathIgnorePatterns [array]
• config.testPathPattern [string]
• config.testRunner [string]
• config.unmockedModulePathPatterns [array]
• config.verbose [boolean]
• config.watchman [boolean]

Globally injected variables

• afterEach(fn)
• beforeEach(fn)
• describe(name, fn)
• expect(value)
• it(name, fn)
• it.only(name, fn) executes only this test. Useful when investigating a failure
• jest
• pit(name, fn) helper for promises
• require(module)
• require.requireActual(module)
• xdescribe(name, fn)
• xit(name, fn)

expect(value)

• .not inverse the next comparison
• .toThrow(?message)
• .toBe(value) comparison using ===
• .toEqual(value) deep comparison. Use jasmine.any(type) to be softer
• .toBeFalsy()
• .toBeTruthy()
• .toBeNull()
• .toBeUndefined()
• .toBeDefined()
• .toMatch(regexp)
• .toContain(string)
• .toBeCloseTo(number, delta)
• .toBeGreaterThan(number)
• .toBeLessThan(number)
• .toBeCalled()
• .toBeCalledWith(arg, um, ents)
• .lastCalledWith(arg, um, ents)

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