Add Origin test

tests/OriginTest.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Intervention\Image\Tests;
+
+use Intervention\Image\Origin;
+
+class OriginTest extends TestCase
+{
+    public function testMediaType(): void
+    {
+        $origin = new Origin();
+        $this->assertEquals('application/octet-stream', $origin->mediaType());
+
+        $origin = new Origin('image/gif');
+        $this->assertEquals('image/gif', $origin->mediaType());
+    }
+}