docs: add a guide to test changes locally (#866)

docs/CONTRIBUTING.md

@@ -7,7 +7,7 @@
 
 ## How to Contribute
 - **Types of Contributions**: There are different ways to contribute to the project. You can contribute by writing code, documentation, reporting bugs, requesting new features, or providing community support in our [Development support channel](https://teams.microsoft.com/l/channel/19%3a5e33f67fe502441f914fbcdc6e2548f5%40thread.skype/Development%2520support%2520-%2520Tegel?groupId=79f9bfeb-73e2-424d-9477-b236191ece5e&tenantId=3bc062e4-ac9d-4c17-b4dd-3aad637ff1ac) or use [GitHub Discussions](/~https://github.com/scania-digital-design-system/tegel/discussions) to start new topic.
-- **First-Time Contributors**: We recommend taking a look on the reported [issues](/~https://github.com/scania-digital-design-system/tegel/issues) here on GitHub. We consider a small bug or improvement a best candidate for first contribution. 
+- **First-Time Contributors**: We recommend taking a look on the reported [issues](/~https://github.com/scania-digital-design-system/tegel/issues) here on GitHub. We consider a small bug or improvement a best candidate for first contribution.
 
 ## Before You Start
 - **Type of Contribution**: If the contribution is a new component or a significant change to an existing one, please get in touch with Tegel's designers and developers beforehand to align on the direction.
@@ -23,6 +23,22 @@
 ## Style Guides
 - **Code Style**: Please read our [Code Style](/~https://github.com/scania-digital-design-system/tegel/blob/main/CODE_STYLE.md) before contributing.
 
+## Testing your changes locally
+To properly test your changes' behaviors in a project, reference your local Tegel instance instead of the published version on the registry
+- **Build Tegel**: Navigate to your current Tegel monorepo directory, and run `npm run build-all`. This will build core Tegel as well as all packages currently supported (Angular, Angular 17 & React).
+- **Linking**: Now building is done, navigate to `packages/core` within Tegel's repository and run `npm link`.
+- **Using linked instance**: We're ready to work now, navigate to your project and run `npm link '@scania/tegel'`. This will create a symlink to the local package, but it won't add Tegel to your dependencies, if it wasn't already. Be sure to install it as dependency before linking, if required.
+
+### (Optional) Testing Packages
+In case you need to test React or Angular packages of Tegel, follow the instructions below replacing `{package}` for **react**, **angular** or **angular-17** respectively.
+- **Building**: Complete the build step for Tegel and verify that the package you plan to test has been built successfully. There are commands available to only build specific packages, i.e., `npm run build-{package}`.
+- **Linking**: After linking core, navigate to `packages/{package}` and execute `npm run link`.
+- **Using linked instances**: In your project run `npm link '@scania/tegel-{package}'` before running `npm link '@scania/tegel'`.
+
+### Unlinking
+- **Removing from Project**: In the project you want the link to be removed execute `npm unlink '@scania/tegel'`. In case any dependency issue arises, delete the `node_modules` folder and run `npm i` to start fresh.
+- **Removing link from npm**: The reference for your local instance is stored globally, to remove it execute `npm uninstall --global '@scania/tegel'`.
+
 ## Testing
 - **Running Tests**: Run `npm run test` to run the test suite. It will execute numerous Playwright tests and might take 15-20 seconds to complete all the tests. Tests run on commit at the moment. A successful test will enable committing.
 - **Writing Tests**: In case a component has been changed or a new feature added, please update or write tests for it. We use [Playwright](https://playwright.dev/docs/writing-tests) for writing tests. Also, take a look at existing tests in our components and see how they are written.