Execute a system command.
Anti-PatternDon’t try to start a web server from
cy.exec()
.Read about best practices here.
Syntax
cy.exec(command) cy.exec(command, options)
Usage
Correct Usage
cy.exec('npm run build')
Arguments
command (String)
The system command to be executed from the project root (the directory that contains the default cypress.json
configuration file).
options (Object)
Pass in an options object to change the default behavior of cy.exec()
.
Option | Default | Description |
---|---|---|
log | true | Displays the command in the Command log |
env | {} | Object of environment variables to set before the command executes (e.g. {USERNAME: 'johndoe'} ). Will be merged with existing system environment variables |
failOnNonZeroExit | true | whether to fail if the command exits with a non-zero code |
timeout | execTimeout | Time to wait for cy.exec() to resolve before timing out
|
Yields
cy.exec()
yields an object with the following properties:
code
stdout
stderr
Examples
Command
cy.exec()
provides an escape hatch for running arbitrary system commands, so you can take actions necessary for your test outside the scope of Cypress. This is great for:
- Running build scripts
- Seeding your test database
- Starting processes
- Killing processes
Run a build command
cy.exec('npm run build').then((result) => { // yields the 'result' object // { // code: 0, // stdout: "Files successfully built", // stderr: "" // } })
Seed the database and assert it was successful
cy.exec('rake db:seed').its('code').should('eq', 0)
Run an arbitrary script and assert its output
cy.exec('npm run my-script').its('stdout').should('contain', 'Done running the script')
Write to a file to create a fixture from response body
cy.server() cy.route('POST', '/comments').as('postComment') cy.get('.add-comment').click() cy.wait('@postComment').then((xhr) => { cy.exec(`echo ${JSON.stringify(xhr.responseBody)} >cypress/fixtures/comment.json`) cy.fixture('comment.json').should('deep.eq', xhr.responseBody) })
Options
Change the timeout
You can increase the time allowed to execute the command, although we don’t recommend executing commands that take a long time to exit.
Cypress will not continue running any other commands until cy.exec()
has finished, so a long-running command will drastically slow down your test cycle.
// will fail if script takes longer than 20 seconds to finish cy.exec('npm run build', { timeout: 20000 })
Choose to not fail on non-zero exit and assert on code and stderr
cy.exec('man bear pig', { failOnNonZeroExit: false }).then((obj) => { expect(obj.code).to.eq(1) expect(obj.stderr).to.contain('No manual entry for bear')
Specify environment variables
cy.exec('echo $USERNAME', { env: { USERNAME: 'johndoe' } }) .its('stdout').should('contain', 'johndoe')
Notes
Commands Must Exit
Commands that do not exit are not supported
cy.exec()
does not support commands that don’t exit, such as:
- Starting a
rails server
- A task that runs a watch
- Any process that needs to be manually interrupted to stop
A command must exit within the execTimeout
or Cypress will kill the command’s process and fail the current test.
Reset timeout via Cypress.config()
You can change the timeout of cy.exec()
for the remainder of the tests by setting the new values for execTimeout
within Cypress.config()
.
Cypress.config('execTimeout', 30000) Cypress.config('execTimeout') // => 30000
Set timeout in the test configuration
You can configure the cy.exec()
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 execTimeout
when complete.
describe('has data available from database', { execTimeout: 90000 }, () => { before(() => { cy.exec('rake db:seed') }) // tests after(() => { cy.exec('rake db:reset') }) })
Rules
Requirements
cy.exec()
requires being chained off ofcy
.cy.exec()
requires the executed system command to eventually exit.cy.exec()
requires that the exit code be0
whenfailOnNonZeroExit
istrue
.
Assertions
cy.exec()
will only run assertions you've chained once, and will not retry.
Timeouts
cy.exec()
can time out waiting for the system command to exit.
Command Log
List the contents of the default cypress.json
configuration file
if (Cypress.platform === 'win32') { cy.exec('print cypress.json') .its('stderr').should('be.empty') } else { cy.exec('cat cypress.json') .its('stderr').should('be.empty') }
The command above will display in the Command Log as:
When clicking on the exec
command within the command log, the console outputs the following: