Add ProcessRunnerTest

tests/Process/ProcessRunnerTest.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Scandalous\Tests\Process;
+
+use PHPUnit\Framework\TestCase;
+use Scandalous\Process\ProcessRunner;
+
+final class ProcessRunnerTest extends TestCase
+{
+    public function testRunExecutesCommandAndReturnsOutput(): void
+    {
+        $runner = new ProcessRunner();
+        $output = $runner->run(['php', '-r', 'echo "hello world";']);
+
+        $this->assertSame('hello world', $output);
+    }
+}