How to reset or clear a spy in Jest?
JavascriptTestingJestjsJavascript Problem Overview
I have a spy that is used in multiple assertions across multiple tests in a suite.
How do I clear or reset the spy so that in each test the method that the spy intercepts is considered not to have been invoked?
For example, how to make the assertion in 'does not run method'
be true?
const methods = {
run: () => {}
}
const spy = jest.spyOn(methods, 'run')
describe('spy', () => {
it('runs method', () => {
methods.run()
expect(spy).toHaveBeenCalled() //=> true
})
it('does not run method', () => {
// how to make this true?
expect(spy).not.toHaveBeenCalled() //=> false
})
})
Javascript Solutions
Solution 1 - Javascript
Thanks to @sdgluck for the answer, though I would like to add to this answer that in my case, I wanted a clear state after each tests since I have multiple tests with same spy. So instead of calling the mockClear()
in previous test(s), I moved it into the afterEach()
(or you can use it with beforeEach
) like so:
afterEach(() => {
jest.clearAllMocks();
});
And finally, my tests are working like they should without the spy being called from previous test. You can also read their documentation for it
Option 2
If you wish to do it from a global level, you could also updated your jest.config.js
(or from package.json
)
module.exports = {
clearMocks: true,
// ...
}
You can read Jest documentation about it
Solution 2 - Javascript
Jest spies have the same API as mocks. The documentation for mocks is here and specifies a method mockClear
which:
> 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.
(emphasis my own)
So we can use mockClear
to "reset" a spy. Using your example:
const methods = {
run: () => {}
}
const spy = jest.spyOn(methods, 'run')
describe('spy', () => {
it('runs method', () => {
methods.run()
expect(spy).toHaveBeenCalled() //=> true
/* clean up the spy so future assertions
are unaffected by invocations of the method
in this test */
spy.mockClear()
})
it('does not run method', () => {
expect(spy).not.toHaveBeenCalled() //=> true
})
})
Solution 3 - Javascript
In case you want to restore the original behavior of a method you had previously added to a spy, you can use the mockRestore method.
Check out the example bellow:
class MyClass {
get myBooleanMethod(): boolean {
return true;
}
}
const myObject = new MyClass();
const mockMyBooleanMethod = jest.spyOn(myObject, 'myBooleanMethod', 'get');
// mock myBooleanMethod to return false
mockMyBooleanMethod.mockReturnValue(false);
// restore myBooleanMethod to its original behavior
mockMyBooleanMethod.mockRestore();
Solution 4 - Javascript
Iterating further on @ghiscoding's answer, you can specify clearMocks
in the Jest config, which is equivalent to calling jest.clearAllMocks()
between each test:
{
...
clearMocks: true,
...
}
See the docs here.
Solution 5 - Javascript
In jest.config.js add mockReset - not clearMocks, as that will not remove any mock implementation between tests (i.e. mockReset is the more cautious option and will remove implementation between tests - which in my opinion is the right thing to do given each tests is supposed to be isolated).
{
...
mockReset: true,
...
}