Execute code in Node via the task plugin event.
Anti-PatternWe do not recommend starting a web server using
cy.task(). Read about best practices here.
Syntax
cy.task(event) cy.task(event, arg) cy.task(event, arg, options)
Usage
Correct Usage
// in test
cy.task('log', 'This will be output to the terminal')
// in plugins file
module.exports = (on, config) => {
on('task', {
log (message) {
console.log(message)
return null
}
})
}
Arguments
event (String)
An event name to be handled via the task event in the pluginsFile.
arg (Object)
An argument to send along with the event. This can be any value that can be serialized by JSON.stringify(). Unserializable types such as functions, regular expressions, or symbols will be omitted to null.
If you need to pass multiple arguments, use an object
// in test
cy.task('hello', { greeting: 'Hello', name: 'World' })
// in plugins/index.js
module.exports = (on, config) => {
on('task', {
// deconstruct the individual properties
hello ({ greeting, name }) {
console.log('%s, %s', greeting, name)
return null
}
})
}
options (Object)
Pass in an options object to change the default behavior of cy.task().
| Option | Default | Description |
|---|---|---|
log | true | Displays the command in the Command log |
timeout | taskTimeout | Time to wait for cy.task() to resolve before timing out
|
Yields
cy.task() yields the value returned or resolved by the task event in the pluginsFile.
Examples
Event
cy.task() provides an escape hatch for running arbitrary Node code, so you can take actions necessary for your tests outside of the scope of Cypress. This is great for:
- Seeding your test database.
- Storing state in Node that you want persisted between spec files.
- Performing parallel tasks, like making multiple http requests outside of Cypress.
- Running an external process.
In the task plugin event, the command will fail if undefined is returned. This helps catch typos or cases where the task event is not handled.
If you do not need to return a value, explicitly return null to signal that the given event has been handled.
Read a file that might not exist
Command cy.readFile() assumes the file exists. If you need to read a file that might not exist, use cy.task.
// in test
cy.task('readFileMaybe', 'my-file.txt').then((textOrNull) => { ... })
// in plugins/index.js
const fs = require('fs')
module.exports = (on, config) => {
on('task', {
readFileMaybe (filename) {
if (fs.existsSync(filename)) {
return fs.readFileSync(filename, 'utf8')
}
return null
}
})
}
Seed a database
// in test
describe('e2e', () => {
beforeEach(() => {
cy.task('defaults:db')
cy.visit('/')
})
it('displays article values', () => {
cy.get('.article-list')
.should('have.length', 10)
})
})
// in plugins/index.js
// we require some code in our app that
// is responsible for seeding our database
const db = require('../../server/src/db')
module.exports = (on, config) => {
on('task', {
'defaults:db': () => {
return db.seed('defaults')
}
})
}
Return a Promise from an asynchronous task
// in test
cy.task('pause', 1000)
// in plugins/index.js
module.exports = (on, config) => {
on('task', {
pause (ms) {
return new Promise((resolve) => {
// tasks should not resolve with undefined
setTimeout(() => resolve(null), ms)
})
}
})
}
Save a variable across non same-origin URL visits
When visiting non same-origin URL, Cypress will change the hosted URL to the new URL, wiping the state of any local variables. We want to save a variable across visiting non same-origin URLs.
We can save the variable and retrieve the saved variable outside of the test using cy.task() as shown below.
// in test
describe('Href visit', () => {
it('captures href', () => {
cy.visit('https://www.mywebapp.com')
cy.get('a').invoke('attr', 'href')
.then((href) => {
// href is not same-origin as current url
// like https://www.anotherwebapp.com
cy.task('setHref', href)
})
})
it('visit href', () => {
cy.task('getHref').then((href) => {
// visit non same-origin url https://www.anotherwebapp.com
cy.visit(href)
})
})
})
// in plugins/index.js
let href
module.exports = (on, config) => {
on('task', {
setHref: (val) => {
return href = val
},
getHref: () => {
return href
}
})
}
Options
Change the timeout
You can increase the time allowed to execute the task, although we do not recommend executing tasks that take a long time to exit.
Cypress will not continue running any other commands until cy.task() has finished, so a long-running command will drastically slow down your test runs.
// will fail if seeding the database takes longer than 20 seconds to finish
cy.task('seedDatabase', null, { timeout: 20000 })
Notes
Tasks must end
Tasks that do not end are not supported
cy.task() does not support tasks that do not end, such as:
- Starting a server.
- A task that watches for file changes.
- Any process that needs to be manually interrupted to stop.
A task must end within the taskTimeout or Cypress will fail the current test.
Tasks are merged automatically
Sometimes you might be using plugins that export their tasks for registration. Cypress automatically merges on('task') objects for you. For example if you are using cypress-skip-and-only-ui plugin and want to install your own task to read a file that might not exist:
// in plugins/index.js file
const skipAndOnlyTask = require('cypress-skip-and-only-ui/task')
const fs = require('fs')
const myTask = {
readFileMaybe (filename) {
if (fs.existsSync(filename)) {
return fs.readFileSync(filename, 'utf8')
}
return null
}
}
// register plugin's task
on('task', skipAndOnlyTask)
// and register my own task
on('task', myTask)
See #2284 for implementation.
Duplicate task keysIf multiple task objects use the same key, the later registration will overwrite that particular key, similar to how merging multiple objects with duplicate keys will overwrite the first one.
Reset timeout via Cypress.config()
You can change the timeout of cy.task() for the remainder of the tests by setting the new values for taskTimeout within Cypress.config().
Cypress.config('taskTimeout', 30000)
Cypress.config('taskTimeout') // => 30000
Set timeout in the test configuration
You can configure the cy.task() timeout within a suite or test by passing the new configuration value within the test configuration.
This will set the timeout throughout the duration of the tests, then return it to the default taskTimeout when complete.
describe('has data available from database', { taskTimeout: 90000 }, () => {
before(() => {
cy.task('seedDatabase')
})
// tests
after(() => {
cy.task('resetDatabase')
})
})
Argument should be serializable
The argument arg sent via cy.task(name, arg) should be serializable; it cannot have circular dependencies (issue #5539). If there are any special fields like Date, you are responsible for their conversion (issue #4980):
// in test
cy.task('date', new Date())
.then((s) => {
// the yielded result is a string
// we need to convert it to Date object
const result = new Date(s)
})
// in plugins/index.js
module.exports = (on, config) => {
on('task', {
date (s) {
// s is a string, so convert it to Date
const d = new Date(s)
// do something with the date
// and return it back
return d
}
})
}
Rules
Requirements
cy.task()requires being chained off ofcy.cy.task()requires the task to eventually end.
Assertions
cy.task()will only run assertions you've chained once, and will not retry.
Timeouts
cy.task()can time out waiting for the task to end.
Command Log
List the contents of the default cypress.json configuration file
cy.task('readJson', 'cypress.json')
The command above will display in the Command Log as:
When clicking on the task command within the command log, the console outputs the following:
History
| Version | Changes |
|---|---|
| 3.0.0 |
cy.task() command added |