Configure Github workflow for testing

Author: martin-helmich

.github/workflows/php.yml

@@ -0,0 +1,40 @@
+name: PHP type checking and unit testing
+
+on: [push]
+
+jobs:
+  build:
+    strategy:      
+      matrix:
+        php: ['7.2', '7.3', '7.4']
+        phpunit: ['8.0', '9.0']
+        exclude:
+          - php: '7.2'
+            phpunit: '9.0'
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+      
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v1
+      with:
+        php-version: ${{ matrix.php }}
+        extensions: mbstring, intl, json
+        coverage: pcov
+    
+    - name: Validate composer.json and composer.lock
+      run: composer validate
+
+    - name: Declare required PHPUnit version
+      run: |
+        composer require --no-update --dev phpunit/phpunit ~${{ matrix.phpunit }}
+
+    - name: Install dependencies
+      run: composer install --prefer-dist --no-progress --no-suggest
+
+    #- name: Run type checker
+    #  run: ./vendor/bin/psalm
+      
+    - name: Run unit tests
+      run: ./vendor/bin/phpunit --testdox