Have UuidInterface extend from JsonSerializable and cover it with a test

src/Uuid.php

@@ -35,7 +35,7 @@ use Ramsey\Uuid\Codec\CodecInterface;
  * @link http://docs.oracle.com/javase/6/docs/api/java/util/UUID.html
  */
 
-class Uuid implements UuidInterface, \JsonSerializable
+class Uuid implements UuidInterface
 {
     /**
      * When this namespace is specified, the name string is a fully-qualified domain name.

src/UuidInterface.php

@@ -16,7 +16,7 @@ namespace Ramsey\Uuid;
 
 use Ramsey\Uuid\Converter\NumberConverterInterface;
 
-interface UuidInterface
+interface UuidInterface extends \JsonSerializable
 {
 
     /**

tests/UuidTest.php

@@ -1742,4 +1742,14 @@ class UuidTest extends TestCase
         $uuid = Uuid::uuid1();
         $uuid->getInteger();
     }
+
+    /**
+     * @covers Ramsey\Uuid\Uuid::jsonSerialize
+     */
+    public function testJsonSerialize()
+    {
+        $uuid = Uuid::uuid1();
+
+        $this->assertEquals('"' . $uuid->toString() . '"', json_encode($uuid));
+    }
 }