Add WordPress unit testing with PHPUnit via wp-env

.github/workflows/ci.yml

@@ -80,6 +80,54 @@ jobs:
       - name: Run PHPStan
         run: composer phpstan
 
+  unit:
+    name: Unit (PHPUnit)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+
+      - name: Cache Composer
+        uses: actions/cache@v4
+        with:
+          path: ~/.composer/cache
+          key: ${{ runner.os }}-composer-unit-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-composer-unit-
+
+      # wp-env downloads WordPress and the core PHPUnit suite into this
+      # directory, which is roughly a gigabyte of git clones. Caching it keeps
+      # `env:start` from re-cloning them on every run. The key covers the
+      # wp-env config and version, because a change to either means different
+      # sources have to be downloaded.
+      - name: Cache wp-env sources
+        uses: actions/cache@v4
+        with:
+          path: ~/.wp-env
+          key: ${{ runner.os }}-wp-env-${{ hashFiles('.wp-env.json', 'package-lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-wp-env-
+
+      # Also installs the Composer dependencies through the postinstall script.
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Start wp-env
+        run: npm run env:start
+
+      - name: Run unit tests
+        run: npm run test:unit
+
+      - name: Stop wp-env
+        if: always()
+        run: npm run env:stop
+
   e2e:
     name: E2E (Playwright)
     runs-on: ubuntu-latest

.gitignore

@@ -62,5 +62,9 @@ package/dist
 # PHPStan result cache
 /.phpstan-cache/
 
+# PHPUnit
+/.phpunit.result.cache
+/phpunit.xml
+
 # Generated docs (published to gh-pages by workflow)
 /docs/

composer.json

@@ -15,7 +15,9 @@
     "phpstan/phpstan": "^2.0",
     "szepeviktor/phpstan-wordpress": "^2.0",
     "php-stubs/wp-cli-stubs": "^2.10",
-    "php-stubs/woocommerce-stubs": "^9.0"
+    "php-stubs/woocommerce-stubs": "^9.0",
+    "phpunit/phpunit": "^9.6@stable",
+    "yoast/phpunit-polyfills": "^1.1@stable"
   },
   "config": {
     "platform": {
@@ -34,6 +36,9 @@
     ],
     "phpstan": [
       "phpstan analyse --memory-limit=-1"
+    ],
+    "test": [
+      "phpunit"
     ]
   },
   "minimum-stability": "dev"