sound-player.js export default class SoundPlayer from '. We'll mock SoundPlayer in our tests for SoundPlayerConsumer. Jest mockReset/resetAllMocks vs mockClear/clearAllMocks We’ve just seen the clearAllMocks definition as per the Jest docs, here’s the mockReset () definition: mockFn. We'll use a contrived example of a class that plays sound files, SoundPlayer, and a consumer class which uses that class, SoundPlayerConsumer. jest.clearAllMocks () Clears the mock.calls and mock.instances properties of all mocks. So you can mock them using mock functions. Therefore, any mock for an ES6 class must be a function or an actual ES6 class (which is, again, another function). Jest can be used to mock ES6 classes that are imported into files you want to test.ĮS6 classes are constructor functions with some syntactic sugar. mockReturnValueOnce ( 'second call' ) Ĭonsole.
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When there are no more mockReturnValueOnce values to use, calls will return a value specified by mockReturnValue. Can be chained so that successive calls to the mock function return different values.
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mockReturnValue ( 43 ) mock ( ) // 43 mockFn.mockReturnValueOnce(value) #Īccepts a value that will be returned for one call to the mock function. exports = class SomeClass ) mockFn.mockReturnValue(value) #Īccepts a value that will be returned whenever the mock function is called. MockImplementation can also be used to mock class constructors: // SomeClass.js mockImplementation (scalar => 42 + scalar ) // or: jest.fn(scalar => 42 + scalar) const a = mockFn ( 0 ) const b = mockFn ( 1 ) Note: jest.fn(implementation) is a shorthand for jest.fn().mockImplementation(implementation). 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. mockFn.mockImplementation(fn) #Īccepts a function that should be used as the implementation of the mock. Thus you have to take care of restoration yourself when manually assigning jest.fn(). This is useful when you want to mock functions in certain test cases and restore the original implementation in others.īeware that mockFn.mockRestore only works when mock was created with jest.spyOn. Removes the mock and restores the initial implementation. To learn more about this and see it in action, see this repo. For this reason, Jest will automatically hoist jest.mock calls to the top of the module (before any imports). You should therefore avoid assigning mockFn.mock to other variables, temporary or not, to make sure you don't access stale data. But often you need to instruct Jest to use a mock before modules use it. This is useful when you want to completely restore a mock back to its initial state.īeware that mockReset will replace mockFn.mock, not just and.
![jest clear mocks jest clear mocks](https://i.stack.imgur.com/o3QS9.png)
![jest clear mocks jest clear mocks](https://miro.medium.com/max/852/1*HlHH9b0JAPvvYn7fVxFh-Q.png)
Resets all information stored in the mock, including any inital implementation given. The clearMocks configuration option is available to clear mocks automatically between tests. You should therefore avoid assigning mockFn.mock to other variables, temporary or not, to make sure you don't access stale data. Often this is useful when you want to clean up a mock's usage data between two assertions.īeware that mockClear will replace mockFn.mock, not just and. Resets all information stored in the and arrays. instances = b // true mockFn.mockClear() # fn ( ) const a = new mockFn ( ) const b = new mockFn ( ) Each call is represented by an array of arguments that were passed during the call.įor 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:, , ] #Īn array that contains all the object instances that have been instantiated from this mock function using new.įor example: A mock function that has been instantiated twice would have the following mock.instances array: const mockFn = jest. An array that represents all calls that have been made into this mock function.