Add missing test for single directory and NS

Please see [here](https://github.com/slimphp/Twig-View/pull/53/files#r55942231)
for the discussion.

tests/TwigTest.php

@@ -57,7 +57,7 @@ public function testSingleNamespaceAndMultipleDirectories()
         $this->assertEquals('Happy Tuesday!', $outputMulti);
     }
 
-    public function testSingleTemplateWithANamespace()
+    public function testArrayWithASingleTemplateWithANamespace()
     {
         $views = new Twig([
             'One' => [
@@ -72,6 +72,19 @@ public function testSingleTemplateWithANamespace()
         $this->assertEquals("<p>Hi, my name is Josh.</p>\n", $output);
     }
 
+    public function testASingleTemplateWithANamespace()
+    {
+        $views = new Twig([
+            'One' => __DIR__.'/templates',
+        ]);
+
+        $output = $views->fetch('@One/example.html', [
+            'name' => 'Josh'
+        ]);
+
+        $this->assertEquals("<p>Hi, my name is Josh.</p>\n", $output);
+    }
+
     public function testMultipleTemplatesWithMultipleNamespace()
     {
         $weekday = (new \DateTimeImmutable('2016-03-08'))->format('l');