If someone has a "bad temper", they get angry often and treat others badly when they do. "Good temper" isn't frequently used, but you will sometimes hear someone being described as having a "good temperament."

"bad temper" and "good temper" are certainly commonly used expressions in English to describe a person's temperament. However, there are also many other words and phrases that can be used to describe someone's personality and temperament, such as "easygoing", "irritable", "calm", "nervous", "moody", and "level-headed", among others. The choice of words used to describe someone's temperament may depend on the speaker's region, cultural background, or personal style.

Someone who does not get angry easily could be described as easy-going, or good-natured, or as having an inexcitable or placid temperament. From collinsdictionary.com : If you describe someone as easygoing, you mean that they are not easily annoyed, worried, or upset, and you think this is a good quality. [approval] ‘He was easygoing and good-natured.’