CI: Add unit tests

.github/workflows/unit-tests.yml

@@ -0,0 +1,67 @@
+name: Unit Tests
+
+on: [push]
+
+jobs:
+  test:
+    name: WP ${{ matrix.wordpress }} on PHP ${{ matrix.php }}
+    runs-on: ubuntu-latest
+    continue-on-error: ${{ matrix.allowed_failure }}
+
+    env:
+      WP_VERSION: ${{ matrix.wordpress }}
+
+    strategy:
+      matrix:
+        include:
+          # Check lowest supported WP version, with the lowest supported PHP.
+          - wordpress: '5.9'
+            php: '7.4'
+            allowed_failure: false
+          # Check latest WP with the highest supported PHP.
+          - wordpress: 'latest'
+            php: 'latest'
+            allowed_failure: false
+          # Check upcoming WP.
+          - wordpress: 'trunk'
+            php: 'latest'
+            allowed_failure: true
+          # Check upcoming PHP - only needed when a new version has been forked (typically Sep-Nov)
+#          - wordpress: 'trunk'
+#            php: 'nightly'
+#            allowed_failure: true
+      fail-fast: false
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up PHP ${{ matrix.php }}
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          extensions: ${{ matrix.extensions }}
+          ini-values: ${{ matrix.ini-values }}
+          coverage: ${{ matrix.coverage }}
+
+      - name: Install Composer dependencies
+        uses: ramsey/composer-install@v3
+        with:
+          composer-options: --ignore-platform-req=php+
+
+      - name: Set up problem matchers for PHP
+        run: echo "::add-matcher::${{ runner.tool_cache }}/php.json"
+
+      - name: Set up problem matchers for PHPUnit
+        run: echo "::add-matcher::${{ runner.tool_cache }}/phpunit.json"
+
+      - name: Show PHP and PHPUnit version info
+        run: |
+          php --version
+          ./vendor/bin/phpunit --version
+
+      - name: Run unit tests (single site)
+        run: composer test-unit
+
+      - name: Run unit tests (multisite)
+        run: composer test-unit-ms

composer.json

@@ -63,6 +63,10 @@
 		"test-unit": [
 			"@php ./vendor/phpunit/phpunit/phpunit --testdox --no-coverage"
 		],
+		"test-unit-ms": [
+			"@putenv WP_MULTISITE=1",
+			"@test-unit"
+		],
 		"test-coverage": [
 			"@php ./vendor/phpunit/phpunit/phpunit --coverage-text --coverage-html=coverage && echo coverage/index.html"
 		]