Warn when writing to 'read only' properties of config

[jennifer-shehane]

Current behavior:

Currently only some of the config values are writable at certain points of a run and it is not clear which are and which aren't. The value simply is not read where necessary if it is not writable.

Honestly, I can't even list out which are readable and writable and when because this has never been documented. I could only guess or dig through code.

Cypress.config()

We briefly noted this in the Cypress.config() doc, but it is sadly lacking a full explanation of which are writable and which are not and when. Previous issue for this: #3422

Some confusion:

• Change userAgent during test Unable to switch userAgent during test run #2100

The other point of confusion is that it appears to be writable, when it's not at all! For example, the below will log the newly set value for userAgent, but it actually takes no effect on the actual userAgent set.

it('sets userAgent?', function () {
  console.log(Cypress.config('userAgent'))
  Cypress.config('userAgent', 'foo')

  // logs foo but does absolutely nothing!
  console.log(Cypress.config('userAgent'))
})

• Change screenshotsFolder during test screenshotsFolder not working correctly  #1525

The test below passes, but Cypress does not indeed change the location of the screenshotsFolder, nor does it throw an error telling you that the screenshotsFolder was not set.

it('screenshots folder not settable', () => {
  Cypress.config('screenshotsFolder', 'cypress/screenshots/desktop')
  expect(Cypress.config('screenshotsFolder')).to.eq('cypress/screenshots/desktop')
  cy.screenshot('homepage_desktop')
})

• Change chromeWebSecurity during test Cypress.Config() does not perform as a expected. #8160

Cypress.config('chromeWebSecurity', true); // Setting up security stuff ON

describe('Load graphql stuff Test', () => {
    it('should visit dashboard', () => {
        cy.visit(`stuff/${stuffId}/stuff/requests?status=0`);
        cy.get('[data-testid="empty-state"]').should('exist');
    });
});

Actual saved screenshot location

Plugins Configuration API

Furthermore, we are expanding upon the use of the config object from within the plugins/index.js https://on.cypress.io/configuration-api - where some of this config is not writable and will not be writable at the time of run as part of #5941

This will have config values that are not writable at time that the plugin is read in like configFile and projectRoot.

Desired behavior:

• We should throw when setting these 'non-writable' config values using Cypress.config
• We should throw/warn? when setting 'non-writable' config values within the Plugins Configuration API.

Related issues

• screenshotsFolder not working correctly screenshotsFolder not working correctly  #1525
• Cypress.config() does not return the complete configuration Cypress.config() does not return the complete configuration #509
• Cypress.config() inside test does not override "blacklistHosts" value Cypress.config() inside test does not override "blacklistHosts" value #7426
• Unable to switch userAgent during test run Unable to switch userAgent during test run #2100

Versions

4.0.1

[jennifer-shehane]

Another related issue trying to overwrite Cypress.config #3422

[jennifer-shehane]

Another strange (maybe related?) issue with trying to overwrite projectId as part of --config flag #6546

[cypress-bot]

Released in 9.2.0.

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Cypress v9.2.0, please open a new issue.