run tests using GitHub actions

.github/workflows/unit-tests.yaml

@@ -0,0 +1,49 @@
+on:
+    - push
+    - pull_request
+
+jobs:
+    phpunit:
+        runs-on: ubuntu-latest
+
+        strategy:
+            matrix:
+                include:
+                    - php: '7.1'
+                      composer: '2.2'
+                    - php: '7.2'
+                      composer: '2.2'
+                    - php: '7.3'
+                      composer: latest
+                    - php: '7.4'
+                      composer: latest
+                    - php: '8.0'
+                      composer: latest
+                    - php: '8.1'
+                      composer: latest
+                    - php: '8.2'
+                      composer: latest
+                    - php: '8.3'
+                      composer: latest
+                    - php: '8.4'
+                      composer: latest
+
+        steps:
+            - name: Checkout the source code
+              uses: actions/checkout@v4
+
+            - name: Set up PHP
+              uses: shivammathur/setup-php@v2
+              with:
+                  php-version: '${{ matrix.php }}'
+
+            - name: Install dependencies
+              uses: php-actions/composer@v6
+              with:
+                  php_version: '${{ matrix.php }}'
+                  version: '${{ matrix.composer }}'
+
+            - name: Run tests
+              run: |
+                  vendor/bin/phpunit
+                  vendor/bin/phpunit test/CommonMarkTestWeak.php || true

test/CommonMarkTestStrict.php

@@ -1,11 +1,13 @@
 <?php
 
+use PHPUnit\Framework\TestCase;
+
 /**
  * Test Parsedown against the CommonMark spec
  *
  * @link http://commonmark.org/ CommonMark
  */
-class CommonMarkTestStrict extends PHPUnit_Framework_TestCase
+class CommonMarkTestStrict extends TestCase
 {
     const SPEC_URL = 'https://raw.githubusercontent.com/jgm/CommonMark/master/spec.txt';