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exec

Execute a system command.

caution
Anti-Pattern

Don'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 Cypress configuration file).

options (Object)

Pass in an options object to change the default behavior of cy.exec().

OptionDefaultDescription
logtrueDisplays 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
failOnNonZeroExittruewhether to fail if the command exits with a non-zero code
timeoutexecTimeoutTime 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.intercept('POST', '/comments').as('postComment')
cy.get('.add-comment').click()
cy.wait('@postComment').then(({ response }) => {
  cy.exec(
    `echo ${JSON.stringify(response.body)} >cypress/fixtures/comment.json`
  )
  cy.fixture('comment.json').should('deep.eq', response.body)
})

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((result) => {
  expect(result.code).to.eq(1)
  expect(result.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 of cy.
  • cy.exec() requires the executed system command to eventually exit.
  • cy.exec() requires that the exit code be 0 when failOnNonZeroExit is true.

Assertions ​

  • cy.exec() will only run assertions you have chained once, and will not retry.

Timeouts ​

  • cy.exec() can time out waiting for the system command to exist.

Command Log​

List the contents of your package.json file

if (Cypress.platform === 'win32') {
  cy.exec('type package.json').its('stderr').should('be.empty')
} else {
  cy.exec('cat package.json').its('stderr').should('be.empty')
}

The command above will display in the Command Log as:

Command Log exec

When clicking on the exec command within the command log, the console outputs the following:

console.log exec

See also​

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