chore: implemement basic tests

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

.github/workflows/php-unit-tests.yml

@@ -0,0 +1,42 @@
+name: PHP Unit Tests
+
+on:
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    
+    steps:
+      - name: Retrieve Server Install Action
+        uses: actions/checkout@v6.0.2
+        with:
+          repository: Nodarx/action-server-install
+          ref: main
+          path: action-server-install
+          github-server-url: https://git.ktrix.dev
+
+      - name: Install Server
+        uses: ./action-server-install
+        with:
+          install-php: 'true'
+          install-node: 'false'
+          php-version: '8.5'
+          node-version: '24'
+          server-path: './server'
+
+      - name: Checkout Pull Request
+        uses: actions/checkout@v6.0.2
+        with:
+          repository: ${{ github.repository }}
+          ref: ${{ github.event.pull_request.head.sha }}
+          path: server/modules/mail_manager
+          github-server-url: https://git.ktrix.dev
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress
+        working-directory: server/modules/mail_manager
+
+      - name: Run tests
+        run: composer test:unit
+        working-directory: server/modules/mail_manager