We're a scrum team of 3 developers, 1 designer, the scrum master, and the product owner. However, we don't have official tester in our team. A problem that is always with us, is that, testing the application and passing those tests and removing bugs has been defined as one of the criteria to consider a PBI (Product Backlog Item) as done.
But the problem is that, no matter how much we (3 developers and 1 designer) try to test the application and implemented use cases, still some bugs are not seen and ruin our presentation (Murphy's lawMurphy's law) to stakeholders.
As a remedy, we recommended that the company hire a new tester. Someone who's job would be testing, and testing only. An official professional tester.
However, the problem is that, scrum master and stakeholders believe that a developer (or a designer) should also be a tester.
Are they right? Should we developers (also designers) be testers too?