Mocking fs.existsSync (or other fs functions)

[kzaiwo]

Since fs is not allowed on Cypress/web browser, I am creating mocks for the fs functions being called in my source (non-test/Electron) code.

For example, fs.existsSync. This method is called many times and will return different responses. So instead of manually mocking and hard-coding all their responses, I just created a task inside the mock so it can be checked dynamically.

window.Cypress.fs = require('fs')
window.Cypress.fs.existsSync = (file) => {
  var retVal = ''
  cy.task('existsSync', file).then((result) => { retVal = result })
  return retVal
}

it('Sample test', () => {
  cy.visit('http://localhost:8080')  
})

And in my plugins.js, the task is simply implemented as:

on('task', {
    existsSync (file) {
      return fs.existsSync(file)
    }
})

But then I am getting an error:

Uncaught Uncaught CypressError: Cypress detected that you returned a promise from a command while also invoking one or more cy commands in that promise.

The command that returned the promise was:

  > `cy.visit()`

The cy command you invoked inside the promise was:

  > `cy.task()`

fs.existsSync() is being called during 'boot-up'.. So it is called during app creation (during cy.visit())

How can I use fs.existsSync??

Help!!!

[jennifer-shehane]

cypress/plugins files run within the context of Node.js, so you can require fs directly there like this example: https://on.cypress.io/task#Read-a-file-that-might-not-exist

But, I'm a bit confused about your use case exactly. How this fs.existsSync is called from your application originally.

[jennifer-shehane]

Unfortunately we have to close this issue due to inactivity. Please comment if there is new information to provide concerning the original issue and we can reopen.