function test_addCopies() { $title = "Three Blind Mice"; $test_book = new Book($title); $test_book->save(); $test_copy = new Copy($amount = 1, $test_book->getId()); $test_copy->save(); $title2 = "Dune"; $test_book2 = new Book($title2); $test_book2->save(); $test_copy->addCopies(1); $result = $test_copy->getAmount(); $this->assertEquals(2, $result); }