...

.github/workflows/ci.yml

@@ -19,6 +19,9 @@ jobs:
                     php-version: ${{ matrix.php-version }}
             -   name: Composer Install
                 run: composer install --no-interaction --no-cache
+            -   name: Make Tests Compatiable With PHPUnit 9+
+                if: contains(fromJSON('["7.3", "7.4", "8.0", "8.1", "8.2"]'), matrix.php-version)
+                run: php tests/make_compatible_with_phpunit9.php
             -   name: PHPUnit
                 run: vendor/bin/phpunit
         strategy:

tests/make_compatible_with_phpunit9.php

@@ -0,0 +1,25 @@
+<?php
+
+/** @var iterable<SplFileInfo> $files */
+$files = new \RecursiveIteratorIterator(new \RecursiveDirectoryIterator(__DIR__));
+foreach ($files as $file) {
+    if ($file->getExtension() === 'php' && $file->getPathname() !== __FILE__) {
+        $fileContents = file_get_contents($file->getPathname());
+        if ($fileContents === false) {
+            throw new \RuntimeException('file_get_contents() failed: ' . $file->getPathname());
+        }
+        $patternToReplacementMap = array(
+            '~(n assertIsArray\([^\)]*\))~' => '$1: void',
+            '~(n assertIsString\([^\)]*\))~' => '$1: void',
+            '~(n assertStringContainsString\([^\)]*\))~' => '$1: void'
+        );
+        $updatedFileContents = preg_replace(
+            array_keys($patternToReplacementMap),
+            array_values($patternToReplacementMap),
+            $fileContents
+        );
+        if (file_put_contents($file->getPathname(), $updatedFileContents) === false) {
+            throw new \RuntimeException('file_put_contents() failed: ' . $file->getPathname());
+        }
+    }
+}