add new test for fetching simple string from graphql

this test was implemented, as I found a bug in my last implementation. So I decided to create a test for this case

tests/GraphQL/Query/SimpleString.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace StudioNet\GraphQL\Tests\GraphQL\Query;
+
+use StudioNet\GraphQL\Definition\Type;
+use StudioNet\GraphQL\Support\Definition\Query;
+
+class SimpleString extends Query {
+	public function getRelatedType() {
+		return Type::string();
+	}
+
+	public function getResolver() {
+		return 'You got this!';
+	}
+}

tests/GraphQLTest.php

@@ -5,6 +5,7 @@
 use GraphQL\Type\Definition\ObjectType;
 use StudioNet\GraphQL\GraphQL;
 use StudioNet\GraphQL\Tests\Entity;
+use StudioNet\GraphQL\Tests\GraphQL\Query\SimpleString;
 use StudioNet\GraphQL\Tests\GraphQL\Query\Viewer;
 
 /**
@@ -130,6 +131,31 @@ public function testCustomQuery() {
 		});
 	}
 
+	/**
+	 * Test simple string query
+	 *
+	 * @return void
+	 */
+	public function testSimpleStringQuery() {
+		factory(Entity\User::class)->create();
+
+		$this->registerAllDefinitions([
+			'query' => [
+				SimpleString::class
+			]
+		]);
+
+		$this->specify('tests simple string query (SimpleString)', function () {
+			$query = 'query { simplestring }';
+
+			$this->assertGraphQLEquals($query, [
+				'data' => [
+					'simplestring' => 'You got this!'
+				]
+			]);
+		});
+	}
+
 	/**
 	 * Test camel case query converter
 	 *