Mock Functions
Имитирующие функции также известны как "шпионы", потому что они позволяют шпионить за поведением функции косвенно вызываемой другим кодом, а не просто тестировать результаты исполнения. Имитирующую функцию можно создать при помощи jest.fn()
. Если реализация не предоставлена, то при вызове имитирующая функция вернет значение undefined
.
Методы #
Справка #
mockFn.mock.calls
#
An array that represents all calls that have been made into this mock function. Each call is represented by an array of arguments that were passed during the call.
For example: A mock function f
that has been called twice, with the arguments f('arg1', 'arg2')
, and then with the arguments f('arg3', 'arg4')
would have a mock.calls
array that looks like this:
[ ['arg1', 'arg2'], ['arg3', 'arg4'], ];
mockFn.mock.instances
#
An array that contains all the object instances that have been instantiated from this mock function using new
.
For example: A mock function that has been instantiated twice would have the following mock.instances
array:
const mockFn = jest.fn(); const a = new mockFn(); const b = new mockFn(); mockFn.mock.instances[0] === a; // true mockFn.mock.instances[1] === b; // true
mockFn.mockClear()
#
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.
The clearMocks
configuration option is available to clear mocks automatically between tests.
mockFn.mockReset()
#
Resets all information stored in the mock, including any inital implementation 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.
mockFn.mockRestore()
#
Removes the mock and restores the initial 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()
.
mockFn.mockImplementation(fn)
#
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)
.
Например:
const mockFn = jest.fn().mockImplementation(scalar => 42 + scalar); // or: jest.fn(scalar => 42 + scalar); const a = mockFn(0); const b = mockFn(1); a === 42; // true b === 43; // true mockFn.mock.calls[0][0] === 0; // true mockFn.mock.calls[1][0] === 1; // true
mockImplementation
can also be used to mock class constructors:
// SomeClass.js module.exports = class SomeClass { m(a, b) {} } // OtherModule.test.js jest.mock('./SomeClass'); // this happens automatically with automocking const SomeClass = require('./SomeClass') const mMock = jest.fn() SomeClass.mockImplementation(() => { return { m: mMock } }) const some = new SomeClass() some.m('a', 'b') console.log('Calls to m: ', mMock.mock.calls)
mockFn.mockImplementationOnce(fn)
#
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.
var 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
When the mocked function runs out of implementations defined with mockImplementationOnce, it will execute the default implementation set with jest.fn(() => defaultValue)
or .mockImplementation(() => defaultValue)
if they were called:
var myMockFn = jest.fn(() => 'default') .mockImplementationOnce(() => 'first call') .mockImplementationOnce(() => 'second call'); console.log(myMockFn(), myMockFn(), myMockFn(), myMockFn()); > 'first call', 'second call', 'default', 'default'
mockFn.mockReturnThis()
#
Just a simple sugar function for:
jest.fn(function() { return this; });
mockFn.mockReturnValue(value)
#
Accepts a value that will be returned whenever the mock function is called.
const mock = jest.fn(); mock.mockReturnValue(42); mock(); // 42 mock.mockReturnValue(43); mock(); // 43
mockFn.mockReturnValueOnce(value)
#
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
.
const myMockFn = jest.fn() .mockReturnValue('default') .mockReturnValueOnce('first call') .mockReturnValueOnce('second call'); console.log(myMockFn(), myMockFn(), myMockFn(), myMockFn()); > 'first call', 'second call', 'default', 'default'