cypress/docs/source/api/commands/stub.md

title, comments

title	comments
stub	false

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

{% note info %} Note: .stub() assumes you are already familiar with our guide: {% url 'Stubs, Spies, and Clocks' stubs-spies-and-clocks %} {% endnote %}

Syntax

cy.stub()
cy.stub(object, method)
cy.stub(object, method, replacerFn)

Usage

cy.stub() cannot be chained off any other cy commands, so should be chained off of cy for clarity.

{% fa fa-check-circle green %} Correct Usage

cy.stub(user, 'addFriend')    

Arguments

{% fa fa-angle-right %} object (Object)

The object that has the method to be replaced.

{% fa fa-angle-right %} method (String)

The name of the method on the object to be wrapped.

{% fa fa-angle-right %} replacerFn (Function)

The function used to replace the method on the object.

Yields {% helper_icon 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 {% url "Sinon.js stub" http://sinonjs.org/%}. All methods found on {% url "Sinon.js" http://sinonjs.org %} spies and stubs are supported.

Examples

Stub

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', function () {
  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

Using cy.stub

{% note info %} {% url "Check out our example recipe testing spying, stubbing and time" stubs-spies-and-clocks-recipe %} {% endnote %}

Alias a stub

Adding an alias using {% url .as() as %} to stubs makes them easier to identify in error messages and Cypress' 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

Automatic reset/restore between tests

cy.stub() creates stubs in a {% url "sandbox" http://sinonjs.org/releases/v2.0.0/sandbox/ %}, so all stubs created are automatically reset/restored between tests without you having to explicitly reset/restore them.

Difference between cy.spy() and cy.stub()

The main difference between cy.spy() and {% url cy.stub() 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.

Assertion Support

Cypress has built-in {% url "sinon-as-promised" https://github.com/bendrucker/sinon-as-promised %} support, so the stubs returned by cy.stub() supports the .resolves and .rejects API provided by sinon-as-promised.

Rules

Requirements {% helper_icon requirements %}

{% requirements parent cy.stub %}

Assertions {% helper_icon assertions %}

{% assertions none cy.stub %}

Timeouts {% helper_icon timeout %}

{% timeouts none cy.stub %}

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:

See also

• {% url .as() as %}
• {% url cy.clock() clock %}
• {% url cy.spy() spy %}
• {% url 'Guide: Stubs, Spies and Clocks' stubs-spies-and-clocks %}
• {% url "Recipe: Controlling Behavior with Spies, Stubs, and Clocks" stubs-spies-and-clocks-recipe %}
• {% url "Recipe: Unit Test - Stubbing Dependencies" unit-testing %}