run tests using GitHub actions

.github/workflows/unit-tests.yaml

@@ -0,0 +1,42 @@
+on:
+    - push
+    - pull_request
+
+jobs:
+    phpunit:
+        runs-on: ubuntu-latest
+
+        strategy:
+            matrix:
+                php:
+                    - '5.3'
+                    - '5.4'
+                    - '5.5'
+                    - '5.6'
+                    - '7.0'
+                    - '7.1'
+                    - '7.2'
+                    - '7.3'
+                    - '7.4'
+                    - '8.0'
+                    - '8.1'
+                    - '8.2'
+                    - '8.3'
+                    - '8.4'
+
+        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
+              run: composer install
+
+            - name: Run tests
+              run: |
+                  vendor/bin/phpunit
+                  vendor/bin/phpunit test/CommonMarkTestWeak.php || true

Parsedown.php

@@ -712,7 +712,7 @@ protected function blockRule($Line)
     #
     # Setext
 
-    protected function blockSetextHeader($Line, ?array $Block = null)
+    protected function blockSetextHeader($Line, array $Block = null)
     {
         if ( ! isset($Block) or isset($Block['type']) or isset($Block['interrupted']))
         {
@@ -850,7 +850,7 @@ protected function blockReference($Line)
     #
     # Table
 
-    protected function blockTable($Line, ?array $Block = null)
+    protected function blockTable($Line, array $Block = null)
     {
         if ( ! isset($Block) or isset($Block['type']) or isset($Block['interrupted']))
         {

composer.json

@@ -17,7 +17,7 @@
         "ext-mbstring": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.35"
+        "phpunit/phpunit": "^4.8|^5.7|^6.5|^7.5|^8.5|^9.6"
     },
     "autoload": {
         "psr-0": {"Parsedown": ""}

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';