Implement LogStream fallback mechanism and add unit tests.

src/Internal/Stream/LogStream.php

@@ -16,7 +16,13 @@ private function __construct(mixed $resource)
 
     public static function from(mixed $resource = null): LogStream
     {
-        return new LogStream(resource: $resource ?? STDERR);
+        if ($resource !== null) {
+            return new LogStream(resource: $resource);
+        }
+
+        $fallback = fopen('php://stderr', 'wb');
+
+        return new LogStream(resource: $fallback);
     }
 
     public function write(string $content): void

tests/Internal/Stream/LogStreamTest.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Test\TinyBlocks\Logger\Internal\Stream;
+
+use PHPUnit\Framework\TestCase;
+use TinyBlocks\Logger\Internal\Stream\LogStream;
+
+final class LogStreamTest extends TestCase
+{
+    /** @noinspection PhpConditionAlreadyCheckedInspection */
+    public function testFromWithoutResourceFallsBackToStderr(): void
+    {
+        /** @Given no resource is provided */
+        /** @When creating a LogStream without a resource */
+        $logStream = LogStream::from();
+
+        /** @Then a LogStream instance should be returned (using stderr as fallback) */
+        self::assertInstanceOf(LogStream::class, $logStream);
+    }
+}