fix(recipes): fix "testing derived state" not working correctly in code sandbox

import selectors extension in spec file instead of through test setup since code sandbox does not support custom jest config files

Author: MrWolfZ

recipes/basics/testing-derived-state/README.md

@@ -12,21 +12,12 @@ Before we start let's install all the packages we need.
 npm i @simplux/core @simplux/selectors redux -S
 ```
 
-We also need to activate the selectors extension by importing the package. You can either add this import to every test file or do it once globally with the mechanism your test framework provides. This recipe uses [Jest](https://jestjs.io/) which allows us to specify a global setup file.
+We also need to activate the selectors extension by importing the package. You can either add this import to every test file or do it once globally with the mechanism your test framework provides (e.g. [Jest](https://jestjs.io/) allows you to configure `setupFiles` where you can place this import).
 
 ```ts
-// in jest.setup.ts
 import '@simplux/selectors'
 ```
 
-```js
-// in jest.config.js
-module.exports = {
-  setupFiles: ['<rootDir>/jest.setup.ts'],
-  // + any other config you need
-}
-```
-
 Now we're ready to go.
 
 Computing derived state for **simplux** modules is done with _selectors_. Selectors are very simple to test as you will see. For this recipe we use a simple counter module with two selectors.

recipes/basics/testing-derived-state/jest.config.js

@@ -6,5 +6,4 @@ module.exports = {
   },
   testMatch: ['<rootDir>/src/**/*.spec.ts'],
   testPathIgnorePatterns: ['node_modules'],
-  setupFiles: ['<rootDir>/jest.setup.ts'],
 }

recipes/basics/testing-derived-state/jest.setup.ts

@@ -1,6 +1,7 @@
 // this code is part of the simplux recipe "testing state changes":
 // https://github.com/MrWolfZ/simplux/tree/master/recipes/basics/testing-state-changes
 
+import '@simplux/selectors'
 import { plus, plusOne, setCounterState } from './counter.module'
 
 describe('counter module', () => {