Search topics implementation (#718)

* Added API support for searching by topic.

* Added accept header for preview mode.

* Fixed parameter definition style.

Author: mikemilano

lib/Github/Api/Search.php

@@ -95,4 +95,21 @@ public function commits($q, $sort = null, $order = 'desc')
 
         return $this->get('/search/commits', ['q' => $q, 'sort' => $sort, 'order' => $order]);
     }
+
+    /**
+     * Search commits by filter (q).
+     *
+     * @link https://developer.github.com/v3/search/#search-topics
+     *
+     * @param string $q the filter
+     *
+     * @return array
+     */
+    public function topics($q)
+    {
+        //This api is in preview mode, so set the correct accept-header
+        $this->acceptHeaderValue = 'application/vnd.github.mercy-preview+json';
+
+        return $this->get('/search/topics', ['q' => $q]);
+    }
 }

test/Github/Tests/Api/SearchTest.php

@@ -196,6 +196,26 @@ public function shouldSearchCommitsRegardingSortAndOrder()
         );
     }
 
+    /**
+     * @test
+     */
+    public function shouldSearchTopics()
+    {
+        $expectedArray = ['total_count' => '0'];
+
+        $api = $this->getApiMock();
+
+        $api->expects($this->once())
+            ->method('get')
+            ->with('/search/topics', ['q' => 'query text'])
+            ->will($this->returnValue($expectedArray));
+
+        $this->assertEquals(
+            $expectedArray,
+            $api->topics('query text')
+        );
+    }
+
     /**
      * @return string
      */