Adds Theme unit tests

tests/Gin/Foundation/ThemeTest.php

@@ -0,0 +1,28 @@
+<?php
+
+use Tonik\Gin\Foundation\Theme;
+
+class ThemeTest extends TestCase
+{
+    /**
+     * @test
+     */
+    public function it_return_same_instance_on_every_access()
+    {
+        $theme = Theme::getInstance();
+
+        $this->assertEquals(Theme::getInstance(), $theme);
+    }
+
+    /**
+     * @test
+     */
+    public function test_binding_and_resolving_from_theme_container()
+    {
+        $theme = Theme::getInstance();
+
+        $theme->bind('key', 'value');
+
+        $this->assertEquals(Theme::getInstance()->get('key'), 'value');
+    }
+}