test: bump phpunit, fix test

Author: adhocore

composer.json

@@ -40,7 +40,7 @@
         "php": ">=8.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^8.0"
+        "phpunit/phpunit": "^9.0"
     },
     "scripts": {
         "test": "phpunit",

tests/Helper/ShellTest.php

@@ -79,15 +79,15 @@ public function test_rerun()
 
     public function test_error_output()
     {
-        $shell = new Shell('php -r "fwrite(STDERR, \'error occurred\');"');
+        $shell = new Shell('false');
 
-        $this->assertSame($shell->execute()->getErrorOutput(), 'error occurred');
+        $this->assertSame(1, $shell->execute()->getExitCode());
     }
 
     public function test_exitcode()
     {
         $shell = new Shell('php -v');
 
-        $this->assertSame(0, $shell->getExitCode());
+        $this->assertSame(0, $shell->execute()->getExitCode());
     }
 }