public function testAddingPrimaryKey()
 {
     $blueprint = new Blueprint('users');
     $blueprint->primary('foo', 'bar');
     $statements = $blueprint->toSql($this->getConnection(), $this->getGrammar());
     $this->assertEquals(1, count($statements));
     $this->assertEquals('alter table "users" add constraint bar primary key ("foo")', $statements[0]);
 }