public function testAddingIndex()
 {
     $blueprint = new Blueprint('users');
     $blueprint->index(['foo', 'bar'], 'baz');
     $statements = $blueprint->toSql($this->getConnection(), $this->getGrammar());
     $this->assertEquals(1, count($statements));
     $this->assertEquals('create index baz on users ( foo, bar )', $statements[0]);
 }