fix: throw when writing to 'read only' properties of config (#18896)

Co-authored-by: Emily Rohrbough <emilyrohrbough@users.noreply.github.com>
2026-02-21 22:50:49 -06:00 · 2021-12-10 11:16:12 -05:00
parent f79bdd665a
commit dd0fc9b9f7
22 changed files with 314 additions and 17 deletions
--- a/cli/types/cypress.d.ts
+++ b/cli/types/cypress.d.ts
@@ -328,7 +328,7 @@ declare namespace Cypress {
    // 60000
    ```
     */
-    config<K extends keyof ConfigOptions>(key: K): ResolvedConfigOptions[K]
+    config<K extends keyof Config>(key: K): Config[K]
    /**
     * Sets one configuration value.
     * @see https://on.cypress.io/config
@@ -337,7 +337,7 @@ declare namespace Cypress {
    Cypress.config('viewportWidth', 800)
    ```
     */
-    config<K extends keyof ConfigOptions>(key: K, value: ResolvedConfigOptions[K]): void
+    config<K extends keyof TestConfigOverrides>(key: K, value: TestConfigOverrides[K]): void
    /**
     * Sets multiple configuration values at once.
     * @see https://on.cypress.io/config
@@ -2879,7 +2879,7 @@ declare namespace Cypress {
    xhrUrl: string
  }

-  interface TestConfigOverrides extends Partial<Pick<ConfigOptions, 'animationDistanceThreshold' | 'baseUrl' | 'defaultCommandTimeout' | 'env' | 'execTimeout' | 'includeShadowDom' | 'requestTimeout' | 'responseTimeout' | 'retries' | 'scrollBehavior' | 'taskTimeout' | 'viewportHeight' | 'viewportWidth' | 'waitForAnimations'>> {
+  interface TestConfigOverrides extends Partial<Pick<ConfigOptions, 'animationDistanceThreshold' | 'baseUrl' | 'blockHosts' | 'defaultCommandTimeout' | 'env' | 'execTimeout' | 'includeShadowDom' | 'numTestsKeptInMemory' | 'pageLoadTimeout' | 'redirectionLimit' | 'requestTimeout' | 'responseTimeout' | 'retries' | 'screenshotOnRunFailure' | 'slowTestThreshold' | 'scrollBehavior' | 'taskTimeout' | 'viewportHeight' | 'viewportWidth' | 'waitForAnimations'>> {
    browser?: IsBrowserMatcher | IsBrowserMatcher[]
    keystrokeDelay?: number
  }
--- a/packages/config/snapshots/index_spec.js
+++ b/packages/config/snapshots/index_spec.js
@@ -23,6 +23,7 @@ exports['src/index .getDefaultValues returns list of public config keys 1'] = {
  "e2e": {},
  "env": {},
  "execTimeout": 60000,
+  "exit": true,
  "experimentalFetchPolyfill": false,
  "experimentalInteractiveRunEvents": false,
  "experimentalSessionSupport": false,
@@ -33,6 +34,8 @@ exports['src/index .getDefaultValues returns list of public config keys 1'] = {
  "ignoreTestFiles": "*.hot-update.js",
  "includeShadowDom": false,
  "integrationFolder": "cypress/integration",
+  "isInteractive": true,
+  "keystrokeDelay": 0,
  "modifyObstructiveCode": true,
  "numTestsKeptInMemory": 50,
  "pageLoadTimeout": 60000,
@@ -97,6 +100,7 @@ exports['src/index .getPublicConfigKeys returns list of public config keys 1'] =
  "e2e",
  "env",
  "execTimeout",
+  "exit",
  "experimentalFetchPolyfill",
  "experimentalInteractiveRunEvents",
  "experimentalSessionSupport",
@@ -107,6 +111,7 @@ exports['src/index .getPublicConfigKeys returns list of public config keys 1'] =
  "ignoreTestFiles",
  "includeShadowDom",
  "integrationFolder",
+  "keystrokeDelay",
  "modifyObstructiveCode",
  "nodeVersion",
  "numTestsKeptInMemory",
@@ -142,5 +147,6 @@ exports['src/index .getPublicConfigKeys returns list of public config keys 1'] =
  "watchForFileChanges",
  "browsers",
  "hosts",
+  "isInteractive",
  "modifyObstructiveCode"
 ]
--- a/packages/config/snapshots/validation_spec.js
+++ b/packages/config/snapshots/validation_spec.js
@@ -154,4 +154,4 @@ Expected \`mockConfigKey\` to be a fully qualified URL (starting with \`http://\

 exports['empty string'] = `
 Expected \`mockConfigKey\` to be a fully qualified URL (starting with \`http://\` or \`https://\`). Instead the value was: \`""\`
-`
+`
--- a/packages/config/lib/index.js
+++ b/packages/config/lib/index.js
@@ -20,6 +20,7 @@ const breakingKeys = _.map(breakingOptions, 'name')
 const defaultValues = createIndex(options, 'name', 'defaultValue')
 const publicConfigKeys = _(options).reject({ isInternal: true }).map('name').value()
 const validationRules = createIndex(options, 'name', 'validation')
+const testConfigOverrideOptions = createIndex(options, 'name', 'canUpdateDuringTestTime')

 module.exports = {
  allowed: (obj = {}) => {
@@ -101,4 +102,16 @@ module.exports = {
      }
    })
  },
+
+  validateNoReadOnlyConfig: (config, onErr) => {
+    let errProperty
+
+    Object.keys(config).some((option) => {
+      return errProperty = testConfigOverrideOptions[option] === false ? option : undefined
+    })
+
+    if (errProperty) {
+      return onErr(errProperty)
+    }
+  },
 }
--- a/packages/config/lib/options.ts
+++ b/packages/config/lib/options.ts
@@ -6,6 +6,10 @@ interface ResolvedConfigOption {
  validation: Function
  isFolder?: boolean
  isExperimental?: boolean
+  /**
+   * Can be mutated with Cypress.config() or test-specific configuration overrides
+   */
+  canUpdateDuringTestTime?: boolean
 }

 interface RuntimeConfigOption {
@@ -13,6 +17,10 @@ interface RuntimeConfigOption {
  defaultValue: any
  validation: Function
  isInternal?: boolean
+  /**
+   * Can be mutated with Cypress.config() or test-specific configuration overrides
+   */
+  canUpdateDuringTestTime?: boolean
 }

 interface BreakingOption {
@@ -72,158 +80,204 @@ const resolvedOptions: Array<ResolvedConfigOption> = [
    name: 'animationDistanceThreshold',
    defaultValue: 5,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'baseUrl',
    defaultValue: null,
    validation: validate.isFullyQualifiedUrl,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'blockHosts',
    defaultValue: null,
    validation: validate.isStringOrArrayOfStrings,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'chromeWebSecurity',
    defaultValue: true,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'clientCertificates',
    defaultValue: [],
    validation: validate.isValidClientCertificatesSet,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'component',
    // runner-ct overrides
    defaultValue: {},
    validation: isValidConfig,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'componentFolder',
    defaultValue: 'cypress/component',
    validation: validate.isStringOrFalse,
    isFolder: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'defaultCommandTimeout',
    defaultValue: 4000,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'downloadsFolder',
    defaultValue: 'cypress/downloads',
    validation: validate.isString,
    isFolder: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'e2e',
    // e2e runner overrides
    defaultValue: {},
    validation: isValidConfig,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'env',
    defaultValue: {},
    validation: validate.isPlainObject,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'execTimeout',
    defaultValue: 60000,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
+  }, {
+    name: 'exit',
+    defaultValue: true,
+    validation: validate.isBoolean,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'experimentalFetchPolyfill',
    defaultValue: false,
    validation: validate.isBoolean,
    isExperimental: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'experimentalInteractiveRunEvents',
    defaultValue: false,
    validation: validate.isBoolean,
    isExperimental: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'experimentalSessionSupport',
    defaultValue: false,
    validation: validate.isBoolean,
    isExperimental: true,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'experimentalSourceRewriting',
    defaultValue: false,
    validation: validate.isBoolean,
    isExperimental: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'experimentalStudio',
    defaultValue: false,
    validation: validate.isBoolean,
    isExperimental: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'fileServerFolder',
    defaultValue: '',
    validation: validate.isString,
    isFolder: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'fixturesFolder',
    defaultValue: 'cypress/fixtures',
    validation: validate.isStringOrFalse,
    isFolder: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'ignoreTestFiles',
    defaultValue: '*.hot-update.js',
    validation: validate.isStringOrArrayOfStrings,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'includeShadowDom',
    defaultValue: false,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'integrationFolder',
    defaultValue: 'cypress/integration',
    validation: validate.isString,
    isFolder: true,
+    canUpdateDuringTestTime: false,
+  }, {
+    name: 'keystrokeDelay',
+    defaultValue: 0,
+    validation: validate.isNumberOrFalse,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'modifyObstructiveCode',
    defaultValue: true,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'nodeVersion',
    validation: validate.isOneOf('bundled', 'system'),
+    canUpdateDuringTestTime: false,
  }, {
    name: 'numTestsKeptInMemory',
    defaultValue: 50,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'pageLoadTimeout',
    defaultValue: 60000,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'pluginsFile',
    defaultValue: 'cypress/plugins',
    validation: validate.isStringOrFalse,
    isFolder: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'port',
    defaultValue: null,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'projectId',
    defaultValue: null,
    validation: validate.isString,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'redirectionLimit',
    defaultValue: 20,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'reporter',
    defaultValue: 'spec',
    validation: validate.isString,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'reporterOptions',
    defaultValue: null,
    validation: validate.isPlainObject,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'requestTimeout',
    defaultValue: 5000,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'resolvedNodePath',
    defaultValue: null,
    validation: validate.isString,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'resolvedNodeVersion',
    defaultValue: null,
    validation: validate.isString,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'responseTimeout',
    defaultValue: 30000,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'retries',
    defaultValue: {
@@ -231,82 +285,101 @@ const resolvedOptions: Array<ResolvedConfigOption> = [
      openMode: 0,
    },
    validation: validate.isValidRetriesConfig,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'screenshotOnRunFailure',
    defaultValue: true,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'screenshotsFolder',
    defaultValue: 'cypress/screenshots',
    validation: validate.isStringOrFalse,
    isFolder: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'slowTestThreshold',
    defaultValue: (options: Record<string, any> = {}) => options.testingType === 'component' ? 250 : 10000,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'scrollBehavior',
    defaultValue: 'top',
    validation: validate.isOneOf('center', 'top', 'bottom', 'nearest', false),
+    canUpdateDuringTestTime: true,
  }, {
    name: 'supportFile',
    defaultValue: 'cypress/support',
    validation: validate.isStringOrFalse,
    isFolder: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'supportFolder',
    defaultValue: false,
    validation: validate.isStringOrFalse,
    isFolder: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'taskTimeout',
    defaultValue: 60000,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'testFiles',
    defaultValue: '**/*.*',
    validation: validate.isStringOrArrayOfStrings,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'trashAssetsBeforeRuns',
    defaultValue: true,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'userAgent',
    defaultValue: null,
    validation: validate.isString,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'video',
    defaultValue: true,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'videoCompression',
    defaultValue: 32,
    validation: validate.isNumberOrFalse,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'videosFolder',
    defaultValue: 'cypress/videos',
    validation: validate.isString,
    isFolder: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'videoUploadOnPasses',
    defaultValue: true,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'viewportHeight',
    defaultValue: 660,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'viewportWidth',
    defaultValue: 1000,
    validation: validate.isNumber,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'waitForAnimations',
    defaultValue: true,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: true,
  }, {
    name: 'watchForFileChanges',
    defaultValue: true,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: false,
  },
 ]

@@ -316,15 +389,18 @@ const runtimeOptions: Array<RuntimeConfigOption> = [
    defaultValue: false,
    validation: validate.isBoolean,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'browsers',
    defaultValue: [],
    validation: validate.isValidBrowserList,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'clientRoute',
    defaultValue: '/__/',
    validation: validate.isString,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'configFile',
    defaultValue: 'cypress.json',
@@ -332,59 +408,76 @@ const runtimeOptions: Array<RuntimeConfigOption> = [
    // not truly internal, but can only be set via cli,
    // so we don't consider it a "public" option
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'devServerPublicPathRoute',
    defaultValue: '/__cypress/src',
    validation: validate.isString,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'hosts',
    defaultValue: null,
    validation: validate.isPlainObject,
+    canUpdateDuringTestTime: false,
+  }, {
+    name: 'isInteractive',
+    defaultValue: true,
+    validation: validate.isBoolean,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'isTextTerminal',
    defaultValue: false,
    validation: validate.isBoolean,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'morgan',
    defaultValue: true,
    validation: validate.isBoolean,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'modifyObstructiveCode',
    defaultValue: true,
    validation: validate.isBoolean,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'namespace',
    defaultValue: '__cypress',
    validation: validate.isString,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'reporterRoute',
    defaultValue: '/__cypress/reporter',
    validation: validate.isString,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'socketId',
    defaultValue: null,
    validation: validate.isString,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'socketIoCookie',
    defaultValue: '__socket.io',
    validation: validate.isString,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'socketIoRoute',
    defaultValue: '/__socket.io',
    validation: validate.isString,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  }, {
    name: 'xhrRoute',
    defaultValue: '/xhrs/',
    validation: validate.isString,
    isInternal: true,
+    canUpdateDuringTestTime: false,
  },
 ]

--- a/packages/config/test/unit/index_spec.js
+++ b/packages/config/test/unit/index_spec.js
@@ -94,7 +94,7 @@ describe('src/index', () => {
        'baseUrl': 'https://',
      }, errorFn)

-      expect(errorFn).to.have.been.callCount(0)
+      expect(errorFn).to.have.callCount(0)
    })

    it('calls error callback if config is invalid', () => {
@@ -125,7 +125,7 @@ describe('src/index', () => {
        configFile: 'config.js',
      })

-      expect(errorFn).to.have.been.callCount(0)
+      expect(errorFn).to.have.callCount(0)
    })

    it('calls error callback if config contains breaking option that should throw an error', () => {
@@ -146,4 +146,31 @@ describe('src/index', () => {
      })
    })
  })
+
+  describe('.validateNoReadOnlyConfig', () => {
+    it('returns an error if validation fails', () => {
+      const errorFn = sinon.spy()
+
+      configUtil.validateNoReadOnlyConfig({ chromeWebSecurity: false }, errorFn)
+
+      expect(errorFn).to.have.callCount(1)
+      expect(errorFn).to.have.been.calledWithMatch(/chromeWebSecurity/)
+    })
+
+    it('does not return an error if validation succeeds', () => {
+      const errorFn = sinon.spy()
+
+      configUtil.validateNoReadOnlyConfig({ requestTimeout: 1000 }, errorFn)
+
+      expect(errorFn).to.have.callCount(0)
+    })
+
+    it('does not return an error if configuration is a non-Cypress config option', () => {
+      const errorFn = sinon.spy()
+
+      configUtil.validateNoReadOnlyConfig({ foo: 'bar' }, errorFn)
+
+      expect(errorFn).to.have.callCount(0)
+    })
+  })
 })
--- a/packages/driver/cypress/integration/commands/fixtures_spec.js
+++ b/packages/driver/cypress/integration/commands/fixtures_spec.js
@@ -101,9 +101,7 @@ describe('src/cy/commands/fixtures', () => {
        return null
      })

-      it('throws if fixturesFolder is set to false', {
-        fixturesFolder: false,
-      }, function (done) {
+      it('throws if fixturesFolder is set to false', { fixturesFolder: false }, function (done) {
        cy.on('fail', () => {
          const { lastLog } = this

--- a/packages/driver/cypress/integration/e2e/testConfigOverrides.spec.js
+++ b/packages/driver/cypress/integration/e2e/testConfigOverrides.spec.js
@@ -377,6 +377,28 @@ describe('testConfigOverrides baseUrl @slow', () => {
  })
 })

+describe('cannot set read-only properties', () => {
+  afterEach(() => {
+    window.top.__cySkipValidateConfig = true
+  })
+
+  it('throws if mutating read-only config with Cypress.config()', (done) => {
+    window.top.__cySkipValidateConfig = false
+    cy.on('fail', (err) => {
+      expect(err.message).to.include('`Cypress.config()` cannot mutate option `chromeWebSecurity` because it is a read-only property.')
+      done()
+    })
+
+    Cypress.config('chromeWebSecurity', false)
+  })
+
+  it('does not throw for non-Cypress config values', () => {
+    expect(() => {
+      Cypress.config('foo', 'bar')
+    }).to.not.throw()
+  })
+})
+
 function hasOnly (test) {
  let curSuite = test.parent
  let hasOnly = false
--- a/packages/driver/cypress/support/defaults.js
+++ b/packages/driver/cypress/support/defaults.js
@@ -2,6 +2,8 @@ const { $ } = Cypress

 const isActuallyInteractive = Cypress.config('isInteractive')

+window.top.__cySkipValidateConfig = true
+
 if (!isActuallyInteractive) {
  // we want to only enable retries in runMode
  // and because we set `isInteractive` above
--- a/packages/driver/src/cypress.ts
+++ b/packages/driver/src/cypress.ts
@@ -1,6 +1,6 @@
 // @ts-nocheck

-import { validate } from '@packages/config'
+import { validate, validateNoReadOnlyConfig } from '@packages/config'
 import _ from 'lodash'
 import $ from 'jquery'
 import * as blobUtil from 'blob-util'
@@ -144,6 +144,24 @@ class $Cypress {
    this.state = $SetterGetter.create({})
    this.originalConfig = _.cloneDeep(config)
    this.config = $SetterGetter.create(config, (config) => {
+      if (!window.top.__cySkipValidateConfig) {
+        validateNoReadOnlyConfig(config, (errProperty) => {
+          let errMessage
+
+          if (this.state('runnable')) {
+            errMessage = $errUtils.errByPath('config.invalid_cypress_config_override', {
+              errProperty,
+            })
+          } else {
+            errMessage = $errUtils.errByPath('config.invalid_test_config_override', {
+              errProperty,
+            })
+          }
+
+          throw new this.state('specWindow').Error(errMessage)
+        })
+      }
+
      validate(config, (errMsg) => {
        throw new this.state('specWindow').Error(errMsg)
      })
--- a/packages/driver/src/cypress/error_messages.ts
+++ b/packages/driver/src/cypress/error_messages.ts
@@ -250,10 +250,16 @@ export default {
      message: `Setting the config via ${cmd('Cypress.config')} failed with the following validation error:\n\n{{errMsg}}`,
      docsUrl: 'https://on.cypress.io/config',
    },
-    'invalid_test_override': {
+    invalid_test_override: {
      message: `The config override passed to your test has the following validation error:\n\n{{errMsg}}`,
      docsUrl: 'https://on.cypress.io/config',
    },
+    invalid_cypress_config_override: {
+      message: `\`Cypress.config()\` cannot mutate option \`{{errProperty}}\` because it is a read-only property.`,
+    },
+    invalid_test_config_override: {
+      message: `Cypress test configuration cannot mutate option \`{{errProperty}}\` because it is a read-only property.`,
+    },
  },

  contains: {
--- a/packages/runner/cypress/integration/reporter.errors.spec.js
+++ b/packages/runner/cypress/integration/reporter.errors.spec.js
@@ -728,9 +728,14 @@ describe('errors ui', () => {
  })

  describe('docs url', () => {
+    after(() => {
+      window.top.__cySkipValidateConfig = false
+    })
+
    const file = 'docs_url_spec.js'
    const docsUrl = 'https://on.cypress.io/viewport'

+    window.top.__cySkipValidateConfig = true
    verify.it('displays as button in interactive mode', { retries: 1 }, {
      file,
      verifyFn () {
--- a/packages/runner/cypress/integration/retries.ui.spec.js
+++ b/packages/runner/cypress/integration/retries.ui.spec.js
@@ -401,8 +401,13 @@ describe('runner/cypress retries.ui.spec', { viewportWidth: 600, viewportHeight:
  })

  describe('can configure retries', () => {
+    after(() => {
+      window.top.__cySkipValidateConfig = false
+    })
+
    const haveCorrectError = ($el) => cy.wrap($el).last().parentsUntil('.collapsible').last().parent().find('.runnable-err').should('contain', 'Unspecified AssertionError')

+    window.top.__cySkipValidateConfig = true
    it('via config value', () => {
      runIsolatedCypress({
        suites: {
--- a/packages/server/test/unit/config_spec.js
+++ b/packages/server/test/unit/config_spec.js
@@ -1430,6 +1430,7 @@ describe('lib/config', () => {
            e2e: { from: 'default', value: {} },
            env: {},
            execTimeout: { value: 60000, from: 'default' },
+            exit: { value: true, from: 'default' },
            experimentalFetchPolyfill: { value: false, from: 'default' },
            experimentalInteractiveRunEvents: { value: false, from: 'default' },
            experimentalSourceRewriting: { value: false, from: 'default' },
@@ -1441,6 +1442,8 @@ describe('lib/config', () => {
            ignoreTestFiles: { value: '*.hot-update.js', from: 'default' },
            includeShadowDom: { value: false, from: 'default' },
            integrationFolder: { value: 'cypress/integration', from: 'default' },
+            isInteractive: { value: true, from: 'default' },
+            keystrokeDelay: { value: 0, from: 'default' },
            modifyObstructiveCode: { value: true, from: 'default' },
            numTestsKeptInMemory: { value: 50, from: 'default' },
            pageLoadTimeout: { value: 60000, from: 'default' },
@@ -1517,6 +1520,7 @@ describe('lib/config', () => {
            downloadsFolder: { value: 'cypress/downloads', from: 'default' },
            e2e: { from: 'default', value: {} },
            execTimeout: { value: 60000, from: 'default' },
+            exit: { value: true, from: 'default' },
            experimentalFetchPolyfill: { value: false, from: 'default' },
            experimentalInteractiveRunEvents: { value: false, from: 'default' },
            experimentalSourceRewriting: { value: false, from: 'default' },
@@ -1550,6 +1554,8 @@ describe('lib/config', () => {
            ignoreTestFiles: { value: '*.hot-update.js', from: 'default' },
            includeShadowDom: { value: false, from: 'default' },
            integrationFolder: { value: 'cypress/integration', from: 'default' },
+            isInteractive: { value: true, from: 'default' },
+            keystrokeDelay: { value: 0, from: 'default' },
            modifyObstructiveCode: { value: true, from: 'default' },
            numTestsKeptInMemory: { value: 50, from: 'default' },
            pageLoadTimeout: { value: 60000, from: 'default' },
--- a/system-tests/snapshots/issue_6407_spec.js
+++ b/system-tests/snapshots/issue_6407_spec.js
@@ -0,0 +1,70 @@
+exports['e2e issue 6407 throws if mutating read-only config with test configuration 1'] = `
+
+====================================================================================================
+
+  (Run Starting)
+
+  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
+  │ Cypress:    1.2.3                                                                              │
+  │ Browser:    FooBrowser 88                                                                      │
+  │ Specs:      1 found (issue_6407_spec.js)                                                       │
+  │ Searched:   cypress/integration/issue_6407_spec.js                                             │
+  └────────────────────────────────────────────────────────────────────────────────────────────────┘
+
+
+────────────────────────────────────────────────────────────────────────────────────────────────────
+                                                                                                    
+  Running:  issue_6407_spec.js                                                              (1 of 1)
+
+
+  1) throws if mutating read-only config with test configuration
+
+  0 passing
+  1 failing
+
+  1) throws if mutating read-only config with test configuration:
+     CypressError: The config override passed to your test has the following validation error:
+
+CypressError: Cypress test configuration cannot mutate option \`chromeWebSecurity\` because it is a read-only property.
+
+https://on.cypress.io/config
+  Error
+      [stack trace lines]
+
+
+
+
+  (Results)
+
+  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
+  │ Tests:        1                                                                                │
+  │ Passing:      0                                                                                │
+  │ Failing:      1                                                                                │
+  │ Pending:      0                                                                                │
+  │ Skipped:      0                                                                                │
+  │ Screenshots:  0                                                                                │
+  │ Video:        true                                                                             │
+  │ Duration:     X seconds                                                                        │
+  │ Spec Ran:     issue_6407_spec.js                                                               │
+  └────────────────────────────────────────────────────────────────────────────────────────────────┘
+
+
+  (Video)
+
+  -  Started processing:  Compressing to 32 CRF                                                     
+  -  Finished processing: /XXX/XXX/XXX/cypress/videos/issue_6407_spec.js.mp4              (X second)
+
+
+====================================================================================================
+
+  (Run Finished)
+
+
+       Spec                                              Tests  Passing  Failing  Pending  Skipped  
+  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
+  │ ✖  issue_6407_spec.js                       XX:XX        1        -        1        -        - │
+  └────────────────────────────────────────────────────────────────────────────────────────────────┘
+    ✖  1 of 1 failed (100%)                     XX:XX        1        -        1        -        -  
+
+
+`
--- a/system-tests/projects/e2e/cypress/integration/issue_6407_spec.js
+++ b/system-tests/projects/e2e/cypress/integration/issue_6407_spec.js
@@ -0,0 +1,4 @@
+/* eslint-disable mocha/no-global-tests, no-undef */
+it('throws if mutating read-only config with test configuration', { chromeWebSecurity: false }, () => {
+  expect(true)
+})
--- a/system-tests/projects/e2e/cypress/integration/session_spec.js
+++ b/system-tests/projects/e2e/cypress/integration/session_spec.js
@@ -1,4 +1,5 @@
 /// <reference types="cypress" />
+window.top.__cySkipValidateConfig = true
 Cypress.config('isInteractive', true)
 Cypress.config('experimentalSessionSupport', true)

--- a/system-tests/projects/integration-outside-project-root/integration/failing_spec.js
+++ b/system-tests/projects/integration-outside-project-root/integration/failing_spec.js
@@ -8,6 +8,8 @@ import { fail, verify } from '../../e2e/cypress/support/util'

 context('validation errors', function () {
  beforeEach(() => {
+    // @ts-ignore
+    window.top.__cySkipValidateConfig = true
    Cypress.config('isInteractive', true)
  })

@@ -16,7 +18,7 @@ context('validation errors', function () {
  })

  verify(this, {
-    line: 15,
+    line: 17,
    column: 8,
    message: 'can only accept a string preset or',
    stack: ['throwErrBadArgs', 'From Your Spec Code:'],
--- a/system-tests/projects/webpack-preprocessor-ts-loader-compiler-options/cypress/integration/failing_spec.ts
+++ b/system-tests/projects/webpack-preprocessor-ts-loader-compiler-options/cypress/integration/failing_spec.ts
@@ -1,5 +1,4 @@
 /// <reference types="cypress" />
-
 /**
 * This tests the error UI for a certain webpack preprocessor setup.
 * It does this by having a test fail and then a subsequent test run that
@@ -16,6 +15,8 @@ import { fail, verify } from '../../../e2e/cypress/support/util'

 context('validation errors', function () {
  beforeEach(() => {
+    // @ts-ignore
+    window.top.__cySkipValidateConfig = true
    // @ts-ignore
    Cypress.config('isInteractive', true)
  })
@@ -26,7 +27,7 @@ context('validation errors', function () {
  })

  verify(this, {
-    line: 25,
+    line: 26,
    column: 8,
    message: 'can only accept a string preset or',
    stack: ['throwErrBadArgs', 'From Your Spec Code:'],
--- a/system-tests/projects/webpack-preprocessor-ts-loader/cypress/integration/failing_spec.ts
+++ b/system-tests/projects/webpack-preprocessor-ts-loader/cypress/integration/failing_spec.ts
@@ -1,5 +1,4 @@
 /// <reference types="cypress" />
-
 /**
 * This tests the error UI for a certain webpack preprocessor setup.
 * It does this by having a test fail and then a subsequent test run that
@@ -16,6 +15,8 @@ import { fail, verify } from '../../../e2e/cypress/support/util'

 context('validation errors', function () {
  beforeEach(() => {
+    // @ts-ignore
+    window.top.__cySkipValidateConfig = true
    // @ts-ignore
    Cypress.config('isInteractive', true)
  })
@@ -26,7 +27,7 @@ context('validation errors', function () {
  })

  verify(this, {
-    line: 25,
+    line: 26,
    column: 8,
    message: 'can only accept a string preset or',
    stack: ['throwErrBadArgs', 'From Your Spec Code:'],
--- a/system-tests/projects/webpack-preprocessor/cypress/integration/failing_spec.js
+++ b/system-tests/projects/webpack-preprocessor/cypress/integration/failing_spec.js
@@ -6,8 +6,11 @@

 import { fail, verify } from '../../../e2e/cypress/support/util'

+window.top.__cySkipValidateConfig = true
 context('validation errors', function () {
  beforeEach(() => {
+    // @ts-ignore
+    window.top.__cySkipValidateConfig = true
    Cypress.config('isInteractive', true)
  })

@@ -16,7 +19,7 @@ context('validation errors', function () {
  })

  verify(this, {
-    line: 15,
+    line: 18,
    column: 8,
    message: 'can only accept a string preset or',
    stack: ['throwErrBadArgs', 'From Your Spec Code:'],
--- a/system-tests/test/issue_6407_spec.js
+++ b/system-tests/test/issue_6407_spec.js
@@ -0,0 +1,14 @@
+const systemTests = require('../lib/system-tests').default
+
+describe('e2e issue 6407', () => {
+  systemTests.setup()
+
+  // https://github.com/cypress-io/cypress/issues/6407
+  it('throws if mutating read-only config with test configuration', function () {
+    return systemTests.exec(this, {
+      spec: 'issue_6407_spec.js',
+      snapshot: true,
+      expectedExitCode: 1,
+    })
+  })
+})