added test with multiple cases for generate

tests/src/Generator/MtRandGeneratorTest.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Ramsey\Uuid\Test\Generator;
+
+use Ramsey\Uuid\Generator\MtRandGenerator;
+
+class MtRandGeneratorTest extends \PHPUnit_Framework_TestCase
+{
+    public function lengthDataProvider()
+    {
+        return [
+            [0],
+            [1],
+            [2],
+            [16],
+            [1000]
+        ];
+    }
+
+    /**
+     * @dataProvider lengthDataProvider
+     */
+    public function testGenerateReturnsStringOfGivenLength($length)
+    {
+        $generator = new MtRandGenerator();
+        $returned = $generator->generate($length);
+        $this->assertEquals($length, strlen($returned));
+    }
+}