spy

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Wrap a method in a spy in order to record calls to and arguments of the function.

Note: .spy() assumes you are already familiar with our guide: Stubs, Spies, and Clocks

Syntax

cy.spy(object, method)

Usage

Correct Usage

cy.spy(user, 'addFriend')

Arguments

object (Object)

The object that has the method to be wrapped.

method (String)

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

Yields

Unlike most Cypress commands, cy.spy() is synchronous and returns a value (the spy) instead of a Promise-like chain-able object.

cy.spy() returns a Sinon.js spy. All methods found on Sinon.JS spies are supported.

Examples

Method

Wrap a method with a spy

// assume App.start calls util.addListeners
cy.spy(util, 'addListeners')
App.start()
expect(util.addListeners).to.be.called

Using cy.spy()

Check out our example recipe testing spying, stubbing and time

Aliases

Adding an alias using .as() to spies makes them easier to identify in error messages and Cypress’ command log.

const obj = {
  foo () {}
}
const spy = cy.spy(obj, 'foo').as('anyArgs')
const withFoo = spy.withArgs('foo').as('withFoo')
obj.foo()
expect(spy).to.be.called
expect(withFoo).to.be.called // purposefully failing assertion

You will see the following in the command log:

spies with aliases

Notes

Restores

Automatic reset/restore between tests

cy.spy() creates spies in a sandbox, so all spies 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.

Assertions

Assertion Support

Cypress has also built-in sinon-chai support, so any assertions supported by sinon-chai can be used without any configuration.

Rules

Requirements

  • cy.spy() requires being chained off of cy.

Assertions

  • cy.spy() cannot have any assertions chained.

Timeouts

  • cy.spy() can not time out.

Command Log

Create a spy, alias it, and call it

const obj = {
  foo () {}
}
const spy = cy.spy(obj, 'foo').as('foo')
obj.foo('foo', 'bar')
expect(spy).to.be.called

The command above will display in the Command Log as:

Command Log spy

When clicking on the spy-1 event within the command log, the console outputs the following:

Command Log

See also