feat: add UI tests to CI

Author: fcasal

.github/workflows/test.yml

@@ -87,6 +87,42 @@ jobs:
               # Allow insiders to fail (may have breaking changes)
               continue-on-error: ${{ matrix.vscode-version == 'insiders' }}
 
+    ui-tests:
+        name: UI Tests (${{ matrix.os }})
+        runs-on: ${{ matrix.os }}
+        strategy:
+            fail-fast: false
+            matrix:
+                os: [ubuntu-latest, macos-latest, windows-latest]
+        steps:
+            - name: Checkout repository
+              uses: actions/checkout@v4
+              with:
+                  persist-credentials: false
+
+            - name: Setup Node.js
+              uses: actions/setup-node@v4
+              with:
+                  node-version: 20
+                  cache: "npm"
+
+            - name: Install dependencies
+              run: npm ci
+
+            - name: Compile extension
+              run: npm run compile
+
+            # Linux requires a virtual display for VS Code / ChromeDriver
+            - name: Run UI tests (Linux)
+              if: runner.os == 'Linux'
+              run: xvfb-run -a npm run test:ui
+              env:
+                  DISPLAY: ":99"
+
+            - name: Run UI tests (macOS/Windows)
+              if: runner.os != 'Linux'
+              run: npm run test:ui
+
     build:
         name: Build Extension
         runs-on: ubuntu-latest