public function testAddMonth() { $date = new DateTime2('2014-01-01'); $date->addMonth(); $this->assertEquals(1, $date->getDay()); $this->assertEquals(2, $date->getMonth()); $returned = $date->addMonth(-2); $this->assertEquals(1, $date->getDay()); $this->assertEquals(12, $date->getMonth()); $this->assertTrue($returned === $date); }