add PostTypeRegistrar tests

.editorconfig

@@ -0,0 +1,8 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space

tests/Registrars/PostTypeRegistrarTest.php

@@ -0,0 +1,24 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use PostTypes\PostType;
+use PostTypes\Registrars\PostTypeRegistrar;
+
+class PostTypeRegistrarTest extends TestCase
+{
+    /** @test */
+    public function canModifyPostType()
+    {
+        $posttype = new PostType('post', [
+            'public' => false,
+        ]);
+
+        $registrar = new PostTypeRegistrar($posttype);
+
+        $options = $registrar->modifyPostType([
+            'public' => true,
+        ], 'post');
+
+        $this->assertEquals(false, $options['public']);
+    }
+}