Add workflow to run PHPUnit tests

.github/workflows/phpunit.yml

@@ -0,0 +1,49 @@
+name: PHPUnit
+
+on:
+  push:
+    branches:
+      - develop
+      - trunk
+    paths:
+      - '**.php'
+  pull_request:
+    branches:
+      - develop
+    paths:
+      - '**.php'
+
+jobs:
+  phpunit:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+
+    - uses: getong/mariadb-action@v1.1
+
+    - name: Setup proper PHP version
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: 7.4
+
+    - name: Get composer cache directory
+      id: composer-cache
+      run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
+
+    - name: Cache dependencies
+      uses: actions/cache@v3
+      with:
+        path: ${{ steps.composer-cache.outputs.dir }}
+        key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+        restore-keys: ${{ runner.os }}-composer-
+
+    - name: Install dependencies
+      run: composer install
+
+    - name: Setup WP Tests
+      run: bash bin/install-wp-tests.sh wordpress_test root '' 127.0.0.1
+
+    - name: PHPUnit
+      run: './vendor/bin/phpunit'

phpunit.xml.dist

@@ -17,4 +17,10 @@
 			<directory suffix=".php">./includes</directory>
 		</whitelist>
 	</filter>
+	<php>
+		<const name="WP_TESTS_MULTISITE" value="1" />
+		<ini name="error_reporting" value="32767" />
+		<ini name="display_errors" value="1" />
+		<ini name="display_startup_errors" value="1" />
+	</php>
 </phpunit>