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Interface MockInstance<T, Y>

Type parameters

  • T

  • Y: any[]

Hierarchy

Index

Properties

Methods

Properties

mock

mock: MockContext<T, Y>

Provides access to the mock's metadata

Methods

getMockName

  • getMockName(): string

  • Returns the mock name string set by calling mockFn.mockName(value).

    Returns string

mockClear

  • mockClear(): void

  • Resets all information stored in the mockFn.mock.calls and mockFn.mock.instances arrays.

    Often this is useful when you want to clean up a mock's usage data between two assertions.

    Beware that mockClear will replace mockFn.mock, not just mockFn.mock.calls and mockFn.mock.instances. You should therefore avoid assigning mockFn.mock to other variables, temporary or not, to make sure you don't access stale data.

    Returns void

mockImplementation

  • mockImplementation(fn?: undefined | ((...args: Y) => T)): this

  • Accepts a function that should be used as the implementation of the mock. The mock itself will still record all calls that go into and instances that come from itself – the only difference is that the implementation will also be executed when the mock is called.

    Note: jest.fn(implementation) is a shorthand for jest.fn().mockImplementation(implementation).

    Parameters

    • Optional fn: undefined | ((...args: Y) => T)

    Returns this

mockImplementationOnce

  • mockImplementationOnce(fn: (...args: Y) => T): this

  • Accepts a function that will be used as an implementation of the mock for one call to the mocked function. Can be chained so that multiple function calls produce different results.

    example

    const myMockFn = jest .fn() .mockImplementationOnce(cb => cb(null, true)) .mockImplementationOnce(cb => cb(null, false));

    myMockFn((err, val) => console.log(val)); // true

    myMockFn((err, val) => console.log(val)); // false

    Parameters

    • fn: (...args: Y) => T
        • (...args: Y): T

        • Parameters

          • Rest ...args: Y

          Returns T

    Returns this

mockName

  • mockName(name: string): this

  • Sets the name of the mock`.

    Parameters

    • name: string

    Returns this

mockRejectedValue

  • Simple sugar function for: jest.fn().mockImplementation(() => Promise.reject(value));

    example

    test('async test', async () => { const asyncMock = jest.fn().mockRejectedValue(new Error('Async error'));

    await asyncMock(); // throws "Async error" });

    Parameters

    Returns this

mockRejectedValueOnce

  • Simple sugar function for: jest.fn().mockImplementationOnce(() => Promise.reject(value));

    example

    test('async test', async () => { const asyncMock = jest .fn() .mockResolvedValueOnce('first call') .mockRejectedValueOnce(new Error('Async error'));

    await asyncMock(); // first call await asyncMock(); // throws "Async error" });

    Parameters

    Returns this

mockReset

  • mockReset(): void

  • Resets all information stored in the mock, including any initial implementation and mock name given.

    This is useful when you want to completely restore a mock back to its initial state.

    Beware that mockReset will replace mockFn.mock, not just mockFn.mock.calls and mockFn.mock.instances. You should therefore avoid assigning mockFn.mock to other variables, temporary or not, to make sure you don't access stale data.

    Returns void

mockResolvedValue

  • Simple sugar function for: jest.fn().mockImplementation(() => Promise.resolve(value));

    Parameters

    Returns this

mockResolvedValueOnce

  • Simple sugar function for: jest.fn().mockImplementationOnce(() => Promise.resolve(value));

    example

    test('async test', async () => { const asyncMock = jest .fn() .mockResolvedValue('default') .mockResolvedValueOnce('first call') .mockResolvedValueOnce('second call');

    await asyncMock(); // first call await asyncMock(); // second call await asyncMock(); // default await asyncMock(); // default });

    Parameters

    Returns this

mockRestore

  • mockRestore(): void

  • Does everything that mockFn.mockReset() does, and also restores the original (non-mocked) implementation.

    This is useful when you want to mock functions in certain test cases and restore the original implementation in others.

    Beware that mockFn.mockRestore only works when mock was created with jest.spyOn. Thus you have to take care of restoration yourself when manually assigning jest.fn().

    The restoreMocks configuration option is available to restore mocks automatically between tests.

    Returns void

mockReturnThis

  • mockReturnThis(): this

  • Just a simple sugar function for:

    example

    jest.fn(function() { return this; });

    Returns this

mockReturnValue

  • mockReturnValue(value: T): this

  • Accepts a value that will be returned whenever the mock function is called.

    example

    const mock = jest.fn(); mock.mockReturnValue(42); mock(); // 42 mock.mockReturnValue(43); mock(); // 43

    Parameters

    • value: T

    Returns this

mockReturnValueOnce

  • mockReturnValueOnce(value: T): this

  • Accepts a value that will be returned for one call to the mock function. Can be chained so that successive calls to the mock function return different values. When there are no more mockReturnValueOnce values to use, calls will return a value specified by mockReturnValue.

    example

    const myMockFn = jest.fn() .mockReturnValue('default') .mockReturnValueOnce('first call') .mockReturnValueOnce('second call');

    // 'first call', 'second call', 'default', 'default' console.log(myMockFn(), myMockFn(), myMockFn(), myMockFn());

    Parameters

    • value: T

    Returns this