stub

Replace a function, record its usage and control its behavior.

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

• cy.stub() is a utility function, and is neither a command nor a query.
• cy.stub() is synchronous and returns a value (the stub) instead of a Promise-like chain-able object. It can be aliased.
• 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

In end-to-end tests, replacing built-in window methods needs to happen after the page is visited, but before the application under test is loaded. You can do this by stubbing functions inside the cy.visit() command onBeforeLoad function.

In Component tests, because the page isn't being reloaded, all you need to do is stub functions before mounting your component.

cy.visit('http://localhost:3000', {
  onBeforeLoad(win) {
    // Stub your functions here
    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')

// Stub your functions here
cy.stub(window, 'prompt').returns('my custom message')

// After that, mount your component
cy.mount(<MyComponent />)

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

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 of cy .

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:

History

See also

• .as()
• cy.clock()
• cy.spy()
• Guide: Stubs, Spies and Clocks
• Recipe: Stubbing, Spying
• Recipe: Unit Test - Stubbing Dependencies
• Stub navigator API in end-to-end tests