docs(svelte): Adds setup information for testing-library-svelte

docs/svelte-testing-library/setup.md

@@ -47,25 +47,52 @@ with any testing framework and runner you're comfortable with.
  }
  ```
 
-5. This is optional but it is recommended, you can install
+5. If you are using ES6 modules in your project you have to add Jest's babel
+ transform setting (it is set by default, but since we are overriding the
+ transform config, we have to add it explicitly)
+
+ 5.1 Install `babel-jest`
+
+ ```bash
+ npm install --save-dev babel-jest
+ ```
+
+ 5.2. Add a basic `.babelrc` configuration
+
+ ```json
+ {
+ "presets": [["@babel/preset-env", { "targets": { "node": "current" } }]]
+ }
+ ```
+
+ 5.3. Update the Jest transform configuration
+
+ ```json
+ "transform": {
+ "^.+\\.js$": "babel-jest",
+ "^.+\\.svelte$": "svelte-jester"
+ },
+ ```
+
+6. This is optional but it is recommended, you can install
  [jest-dom](https://github.com/testing-library/jest-dom) to add handy
  assertions to Jest
 
- 5.1 Install jest-dom
+ 6.1 Install jest-dom
 
  ```
  npm install --save-dev @testing-library/jest-dom
  ```
 
- 5.2 Add the following to your Jest configuration in `package.json`
+ 6.2 Add the following to your Jest configuration in `package.json`
 
  ```json
  {
  "setupFilesAfterEnv": ["@testing-library/jest-dom/extend-expect"]
  }
  ```
 
-6. Create your component + test file (checkout the rest of the docs to see how)
+7. Create your component + test file (checkout the rest of the docs to see how)
  and run it
 
  ```
@@ -78,9 +105,9 @@ To use Typescript, you'll need to install and configure `svelte-preprocess` and
 `ts-jest`. For full instructions, see the
 [`svelte-jester`](https://github.com/mihar-22/svelte-jester#typescript) docs.
 
-## Babel / Preprocessors
+## Preprocessors
 
-If you'd like to also include [Babel](https://babeljs.io/) or any
+If you'd like to also include any
 [Svelte preprocessors](https://github.com/sveltejs/svelte-preprocess) then
 simply follow the instructions over at
 [svelte-jester](https://github.com/mihar-22/svelte-jester#babel).