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://memory', 'wb+');
+
+        return new LogStream(resource: $fallback);
     }
 
     public function write(string $content): void

tests/Internal/Stream/LogStreamTest.php

@@ -0,0 +1,42 @@
+<?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
+{
+    public function testFromWithCustomResource(): void
+    {
+        /** @Given a custom writable stream */
+        $stream = fopen('php://memory', 'r+');
+
+        /** @When creating a LogStream with the custom resource */
+        $logStream = LogStream::from(resource: $stream);
+
+        /** @Then it should write content to the provided stream */
+        $logStream->write('custom resource test');
+
+        rewind($stream);
+        $output = stream_get_contents($stream);
+
+        self::assertSame('custom resource test', $output);
+
+        fclose($stream);
+    }
+
+    public function testFromWithNullFallsBackToStderr(): void
+    {
+        /** @Given no resource is provided */
+        /** @When creating a LogStream without arguments */
+        $logStream = LogStream::from();
+
+        /** @Then it should be created successfully and be writable without errors */
+        $logStream->write('fallback test');
+
+        self::assertTrue(true);
+    }
+}