Add some help for working from the root

Author: juliasilge

apps/vscode/CONTRIBUTING.md

@@ -7,14 +7,19 @@ yarn             # install dependencies
 yarn dev-vscode  # run development/debug version of extension
 ```
 
+Run the extension tests with:
+
+```sh
+yarn test-vscode # compile the test files and run them with the vscode-test CLI
+```
+
 Install the dev version of the extension in VS Code or Positron with:
 
 ```sh
 yarn install-vscode
 yarn install-positron
 ```
 
-
 # Debugging the extension
 
 The extension must have been built in dev mode (see the build section). The `dev` build flag is essential for debugging:

package.json

@@ -11,6 +11,7 @@
     "build": "turbo run build",
     "dev-writer": "turbo run dev --filter writer*",
     "dev-vscode": "turbo run dev --filter quarto...",
+    "test-vscode": "cd apps/vscode && yarn test",
     "install-vscode": "cd apps/vscode && yarn install-vscode",
     "install-positron": "cd apps/vscode && yarn install-positron",
     "lint": "turbo run lint",