I am a web developer in a team of 6 and our company is global. Our method of work consists a planned "software-release day" almost every 2 weeks.
Every developer's work in our team has to go through the QA. However, the QA co-worker (let's call him Bob) is only 6 hours per day at the office, due to his contract's nature.
Before each release he has to go through our work and test if everything's in order. However, when the clock hits 14:00 Bob leaves immediately because he has to pick up his kid from school. However the tests have to be delivered the same day, at the end of business.
Bob comes to me and says in a very stressful way that the tests must be completed and delivered to the next responsible for our release. This is where I come in, although it's not my task. Sometimes I even end up testing my own code which is very bad for QA standards. None of the other developers is dealing with it, which leaves me doing overtime to finish his work. For him it is granted that I will do it and I am not aware how he came up with this.
How can I politely stop this?