Replace a function, record its usage and control its behavior.
Note:
.stub()assumes you are already familiar with our guide: Stubs, Spies, and Clocks
Syntax
cy.stub() cy.stub(object, method) cy.stub(object, method, replacerFn)
Usage
Correct Usage
cy.stub(user, 'addFriend')
Arguments
object (Object)
The object that has the method to be replaced.
method (String)
The name of the method on the object to be wrapped.
replacerFn (Function)
The function used to replace the method on the object.
Yields
Unlike most Cypress commands, cy.stub() is synchronous and returns a value (the stub) instead of a Promise-like chain-able object.
cy.stub() returns a Sinon.js stub. All methods found on Sinon.js spies and stubs are supported.
Examples
Method
Create a stub and manually replace a function
// assume App.start calls util.addListeners util.addListeners = cy.stub() App.start() expect(util.addListeners).to.be.called
Replace a method with a stub
// assume App.start calls util.addListeners cy.stub(util, 'addListeners') App.start() expect(util.addListeners).to.be.called
Replace a method with a function
// assume App.start calls util.addListeners
let listenersAdded = false
cy.stub(util, 'addListeners', () => {
listenersAdded = true
})
App.start()
expect(listenersAdded).to.be.true
Specify the return value of a stubbed method
// assume App.start calls util.addListeners, which returns a function // that removes the listeners const removeStub = cy.stub() cy.stub(util, 'addListeners').returns(removeStub) App.start() App.stop() expect(removeStub).to.be.called
Replace built-in window methods like prompt
// assume App.start uses prompt to set the value of an element with class "name"
cy.visit('http://localhost:3000', {
onBeforeLoad(win) {
cy.stub(win, 'prompt').returns('my custom message')
}
})
App.start()
cy.window().its('prompt').should('be.called')
cy.get('.name').should('have.value', 'my custom message')
Disable logging to Command Log
You can chain a .log(bool) method to disable cy.stub() calls from being shown in the Command Log. This may be useful when your stubs are called an excessive number of times.
const obj = {
foo () {}
}
const stub = cy.stub(obj, 'foo').log(false)
More cy.stub() examples
Check out our example recipe testing spying, stubbing and time
Aliases
Adding an alias using .as() to stubs makes them easier to identify in error messages and Cypress’s command log.
const obj = {
foo () {}
}
const stub = cy.stub(obj, 'foo').as('anyArgs')
const withFoo = stub.withArgs('foo').as('withFoo')
obj.foo()
expect(stub).to.be.called
expect(withFoo).to.be.called // purposefully failing assertion
You will see the following in the command log:
Notes
Restores
Automatic reset/restore between tests
cy.stub() creates stubs in a sandbox, so all stubs created are automatically reset/restored between tests without you having to explicitly reset/restore them.
Differences
Difference between cy.spy() and cy.stub()
The main difference between cy.spy() and cy.stub() is that cy.spy() does not replace the method, it only wraps it. So, while invocations are recorded, the original method is still called. This can be very useful when testing methods on native browser objects. You can verify a method is being called by your test and still have the original method action invoked.
Rules
Requirements
cy.stub()requires being chained off ofcy.
Assertions
cy.stub()cannot have any assertions chained.
Timeouts
cy.stub()cannot time out.
Command Log
Create a stub, alias it, and call it
const obj = {
foo () {}
}
const stub = cy.stub(obj, 'foo').as('foo')
obj.foo('foo', 'bar')
expect(stub).to.be.called
The command above will display in the Command Log as:
When clicking on the (stub-1) event within the command log, the console outputs the following:
