Cypress config files should support "extends" option

Desired behavior:

TypeScript config files (tsconfig.json) allow the user to “extend” an existing file, e.g.:

tsconfig.json:

{
  "someOption": "value",
  "someOption2": "value2"
}

tsconfig.test.json:

{
  "extends": "./tsconfig.json",
  "someOption": "value3"
}

The end result is that the TypeScript compiler sees tsconfig.test.json as this:

{
  "someOption": "value3",
  "someOption2": "value2"
}

This allows the config files to remain DRY and avoid duplicating data, but still have multiple files for different scenarios.

Now that cypress has the --config-file option, I think cypress.json should support this too.

[Camo30]

Unfortunately the plugin from @bahmutov doesn’t work in my environment. This should work out of the box

[ling1726]

@bahmutov @jennifer-shehane An extra scenario where this would be useful: in Fluent UI we have a lerna monorepo. We would like each package to be responsible for its own cypress tests, but would like to have one place for test helpers and configurations. At the same time a package should be able to extend or override the base config.

It seems too heavy weight to create a completely new package in the monorepo just to share cypress utilities, if it’s possible to do path extension

packages/
├── scripts/ cypress
│   ├── fixtures
│   ├── plugins
│   ├── support
│   ├── cypress.json // base
├── menu/
│   ├── package.json
│   ├── Menu.spec.ts
|   ├── cypress.json // extends root
└── button/
    ├── package.json
    ├── Button.spec.ts
    ├── cypress.json // etends root